Tests were made of the genotoxic activities of diesel emission particles (DEP) dispersed in a primary component of pulmonary surfactant, dipalmitoyl-lecithin (DPL), and in dimethyl-sulfoxide (DMSO) in an attempt to provide short term in-vitro genotoxicity assays which mimic the condition of respirable DEP deposited on the bronchoalveolar surface in the lung. The micronucleus induction and phagocytic capacity of Chinese-hamster lung (V79) and ovary (CHO) cells treated with DEP were examined. Treatment with DMSO supernatant resulted in an increase in micronucleus frequencies in both V79 and CHO cells at all concentrations tested (5, 34, 68, and 136 micrograms/milliliter (microg/ml)). However, treatment with DMSO sediment caused an increase in micronucleus frequency only in V79 cells at 34microg/ml, but not at the two higher concentrations. The DPL supernatant caused an increase of micronucleus frequency only in CHO cells, and only at the 34microg/ml concentration. In V79 cells, only at 68microg/ml was the micronucleus frequency statistically different from control levels. In general, CHO cells gave a higher response than did V79 cells. N-Methyl-N-nitro-N- nitrosoguanidine treatment resulted in the pulverization of the nucleus in many CHO cells. Data gathered from the study were used to determine a possible correlation between phagocytosis and genotoxicity and to compare the sensitivity of the two commonly used cell lines to DEP.