The genotoxic activity of coal dust extract nitrosated with sodium- nitrite (7632000) was studied in male CD1-mice using the in-vivo sister chromatid exchange (SCE) assay system with five different concentrations (5 to 80 grams/kilogram (g/kg)) of extract. SCEs in bone marrow cells following single administration of coal dust extract, sodium-nitrite, and nitrosated coal dust extract were slightly higher than controls, in an apparently dose related manner; these differences were not significant. After two oral administrations, the differences were still not significant, except in the case of nitrosated coal-dust. Bromodeoxyuridine differential staining was also used to assess the effects of test compounds on cell replication. Generally, the experimental treatments did not induce cell cycle inhibition. The same extracts were also tested for mutagenicity in Salmonella-typhimurium (TA-98). The coal dust extract was either nonmutagenic or weakly mutagenic and sodium- nitrite was nonmutagenic both with and without S9 activation. On the other hand, nitrosated coal dust extract produced relatively more histidine(+) revertants per plate in a dose related manner both with and without S9 activation. Data on cell kinetics indicated the nontoxicity of treatments. The authors conclude that these studies provide additional evidence of the genotoxicity of nitrosated coal dust, and they recommend chronic studies to evaluate its potential effects on humans.