PA-1 cell line is derived from human ovary teratocarcinoma. When it grows in 10% fetal calf serum, it can be induced to differentiate by 10(-5) mol/L retinoic acid (RA). Some morphological changes can be observed after RA induction. By immunostaining of cultured cells, we found that the expression and distribution pattern of desmin and some extracellular matrix molecules, such as fibronectin, laminin and tenascin, had been changed after induction, and these changes were associated with the morphological changes. Cell growth study showed that RA treatment had no effects on growth and autocrine activities of PA-1 cells. These results suggest that some PA-1 cells were induced to differentiate along muscle cells pathway by RA.