The article presents a study on the use of secrecy in Argentine biopharmaceutical firms that innovate through public-private cooperation. When innovation is achieved by cooperating with public and external sources of knowledge, the company is exposed to higher risks that critical knowledge leaks out to potential competitors, undermining the effectiveness of secrecy. To investigate this issue, study cases have been conducted on firms whose innovation projects are carried out by cooperating with public R&D institutions. The results suggest that the specific features of cooperation determine different possibilities for firms to face those risks, adapt its strategy of appropriation and protect the generated knowledge.