Induction of sister chromatid exchanges (SCEs) by coal dust and tobacco snuff in human peripheral lymphocytes was examined. Peripheral lymphocytes from three healthy nonsmoking donors were incubated with dichloromethane plus acetone or aqueous extracts of anthracite, bituminous, subbituminous coal, lignite, or peat dust or snuff alone or in combination. The cells were scored for SCEs. The effects on cell cycling were determined. Snuff at 4920microg/ml induced a 59% increase in SCE frequency. Coal dust alone caused an average maximum increase in SCE frequency of almost twice the control frequency. Coal dust plus snuff caused a maximum three fold increase in SCE frequency. The highest combined dose induced cell cycle delay in all three donors. When analyzed by coal type, organic solvent extracts of bituminous and subbituminous coal produced the most SCEs, followed by lignite and peat. Organic anthracite extracts did not induce SCEs. Organic extracts of all five coal types induced cell cycle delays. Aqueous extracts of bituminous coal, lignite, and peat induced SCEs. The subbituminous dust extract did not induce SCEs. Anthracite showed an equivocal response, inducing SCEs in only one subject. Organic solvent extracts of bituminous and subbituminous coal dust were tested with lymphocytes from five other donors to assess variability in the responses. The extracts induced dose related increases in SCE frequency in each donor; however, the magnitude of the responses varied significantly between donors. Analysis of variance indicated that the responses were influenced by dose, coal type, and donor. The authors conclude that coal dust and snuff cause a synergistic induction of SCEs in human peripheral lymphocytes. Use of snuff may create an additional health hazard for some coal miners.