Primary human lung adenocarcinomas were divided into two groups according to the degree of histologic differentiation: G2-moderately and G3-poorly differentiated tumors. Each group was compared with normal lung tissue in respect to prolidase activity, its ability to interact with specific antibody, free proline and beta 1 integrin subunit content as well as ability of beta 1 integrin subunit to interact with specific antibody. It was found that prolidase activity in lung adenocarcinomas G3, was significantly elevated in comparison to normal lung tissue. In lung adenocarcinoma G2 no significant changes in the enzyme activity were observed. Increase in the enzyme activity was accompanied by increase of free proline content in the tissues. The western blot analysis revealed that prolidase of lung adenocarcinomas is identical to prolidase originated in control lung tissue. It was noticed that elevated activity of prolidase in adenocarcinomas G3 was accompanied by its high expression. In respect to beta 1 integrin expression, known to play an important role in metastasis, no difference was found between adenocarcinoma groups and the control lung tissue. The presented data suggest that the level of prolidase activity in lung adenocarcinoma may serve as a more sensitive marker for the histologic degree of malignancy, than the level of beta 1 integrin expression.