The excretion of thioethers was determined in urine of nurses who were handling cytotoxic drugs. An occupationally non-exposed group served as control. The results showed a significant difference in urinary thioether excretion between the exposed and control persons (P less than 0.05). In both groups, however, higher thioether excretion was found in smokers; both exposed smoking nurses and smoking controls had significantly higher urinary thioether levels than the non-smoking exposed and control persons. The results suggested a synergistic effect of smoking with exposure to cytostatic drugs: thioether excretion of urine from exposed smokers was significantly higher than that of control smokers (P less than 0.05). There was no difference in urinary thioether levels between the non-smoking exposed and control persons (P greater than 0.05). In conclusion, smoking nurses handling cytostatic drugs, have a greater risk than non-smoking colleagues and protective intervention methods should be used by smoking as well as non-smoking hospital employees.