Two vinyl monomers, styrene and vinylacetate, were tested for their ability to induce chromosome aberrations in cultured human lymphocytes. The effects of a 24-h treatment (48 h after culture initiation) were studied both in whole-blood cultures (with 2 X 10(8) erythrocytes/ml) and in isolated lymphocytes (with 4000 erythrocytes/ml). Styrene produced a clear dose-dependent increase in chromatid-type aberrations in whole-blood cultures (0.5-6 mM) and a weaker effect in cultures of isolated lymphocytes (1-4 mM). A statistically significant elevation in aberrations was observed at 2 mM in the former culture type and at 1 mM in the latter. These results support earlier studies on the importance of erythrocytes in the metabolic activation of styrene, but also suggest that a part of this activation occurs in the lymphocytes themselves. Vinylacetate (0.125-2 mM), the more potent clastogen of the two monomers tested, induced a distinct dose-dependent increase in chromatid-type aberrations and a slight elevation in chromosome-type breaks in both culture types. The lowest concentration giving a positive result was 0.25 mM. The clastogenic effects of vinylacetate were somewhat more pronounced in isolated lymphocytes than in whole blood. Vinylacetate is known to be rapidly hydrolyzed in vitro to acetaldehyde, which probably explains the positive result.