Smooth muscle cells in the thickened intima of the aorta also expressed sis, mye, and c-fos, in addition to collagen types I, III, IV and type V. In the cultures of smooth muscle cells isolated from human aorta, collagen I, III and gelatinase were produced without any other special conditions for the culture. In the presence of PDGF, collagen type V and collagenase production was detected in the culture. Oncogene expression was not detected in the cultured cells when tested by the indirect immunofluorescence technique. Immortalized smooth muscle cells with SV 40 expressed myc, SV 40 large T antigen, and p53 without inhibition of collagen and collagenolytic enzymes production.