The following is a list of biotech companies that have, on average, seen more insider buying than insider selling over the last two years (excluding exercised options). For each company we'll list the average number of shares purchased by insiders on the open market over the last two years.

If you're interested in biotech investing, this list might offer an interesting starting point. Insiders seem to be enthusiastic about the prospects of their employers. Do they know something we don't? Full details below.

Insider data sourced from Fidelity, short float and performance data sourced from Finviz.

*Interactive Chart: Press Play to compare changes in analyst ratings over the last two years for the top six stocks mentioned below. Analyst ratings sourced from Zacks Investment Research. Note: The numbers on top of items represent the forward P/E ratio, if available.*

The list has been sorted by the average number of shares purchased by insider per year over the last two years.

**1. GTX Inc. (NASDAQ:GTXI):** Market cap of $146.58M. Insiders purchased an average of 2,141,258 shares per year over the last two years. Short float at 12.16%, which implies a short ratio of 15.19 days. The stock has lost -28.11% over the last year.

** 2. Anadys Pharmaceuticals Inc. (NASDAQ:ANDS): **Market cap of $76.51M. Insiders purchased an average of 1,967,596 shares per year over the last two years. Short float at 1.64%, which implies a short ratio of 1.35 days. The stock has lost -35.89% over the last year.

**3. MannKind Corp. (NASDAQ:MNKD):**Market cap of $640.07M. Insiders purchased an average of 1,746,833 shares per year over the last two years. Short float at 28.23%, which implies a short ratio of 5.44 days. The stock has lost -50.39% over the last year.

**Market cap of $1.73B. Insiders purchased an average of 1,460,235 shares per year over the last two years. Short float at 13.46%, which implies a short ratio of 14.46 days. The stock has gained 63.19% over the last year.**

4. Seattle Genetics Inc. (NASDAQ:SGEN):

4. Seattle Genetics Inc. (NASDAQ:SGEN):

**5. QLT Inc. (NASDAQ:QLTI):**Market cap of $357.98M. Insiders purchased an average of 1,024,538 shares per year over the last two years. Short float at 1.53%, which implies a short ratio of 2.92 days. The stock has gained 53.85% over the last year.

**Market cap of $302.64M. Insiders purchased an average of 923,474 shares per year over the last two years. Short float at 10.43%, which implies a short ratio of 7.49 days. The stock has gained 138.76% over the last year.**

6. Chelsea Therapeutics International Ltd. (NASDAQ:CHTP):

6. Chelsea Therapeutics International Ltd. (NASDAQ:CHTP):

**7. ZIOPHARM Oncology, Inc. (NASDAQ:ZIOP):**Market cap of $290.87M. Insiders purchased an average of 366,383 shares per year over the last two years. Short float at 7.75%, which implies a short ratio of 10.42 days. The stock has gained 97.04% over the last year.

**8. Inhibitex Inc. (NASDAQ:INHX):**Market cap of $155.83M. Insiders purchased an average of 282,140 shares per year over the last two years. Short float at 2.58%, which implies a short ratio of 3.37 days. The stock has gained 138.1% over the last year.

**Market cap of $440.04M. Insiders purchased an average of 242,795 shares per year over the last two years. Short float at 6.23%, which implies a short ratio of 12.22 days. The stock has lost -13.78% over the last year.**

9. Optimer Pharmaceuticals, Inc. (NASDAQ:OPTR):

9. Optimer Pharmaceuticals, Inc. (NASDAQ:OPTR):

**10. Exelixis, Inc. (NASDAQ:EXEL):**Market cap of $984.18M. Insiders purchased an average of 241,350 shares per year over the last two years. Short float at 7.28%, which implies a short ratio of 4.01 days. The stock has gained 37.65% over the last year.

**11. Medivation, Inc. (NASDAQ:MDVN):**Market cap of $479.83M. Insiders purchased an average of 188,146 shares per year over the last two years. Short float at 4.7%, which implies a short ratio of 5.36 days. The stock has lost -58% over the last year.

**12. PharmAthene, Inc. (NYSEMKT:PIP):**Market cap of $133.78M. Insiders purchased an average of 174,765 shares per year over the last two years. Short float at 6.98%, which implies a short ratio of 1.19 days. The stock has gained 62.69% over the last year.

**13. Xenoport, Inc. (NASDAQ:XNPT):**Market cap of $247.7M. Insiders purchased an average of 68,150 shares per year over the last two years. Short float at 9.16%, which implies a short ratio of 7.84 days. The stock has lost -56.33% over the last year.

**Disclosure:**I have no positions in any stocks mentioned, and no plans to initiate any positions within the next 72 hours.