Cytogenetic and haematological parameters were studied in 31 oil exposed workers and 31 office workers matched for age and smoking, all men employed by a Norwegian cable manufacturing company. Information was obtained about tobacco and alcohol consumption, infections, allergies, chronic diseases, use of medicines, and exposure to radiography. A decrease in the absolute lymphocyte counts was observed in the most heavily exposed subgroup (p less than 0.05) but no other significant differences were found between exposed workers and referents. The influence of non-occupational variables on the cytogenetic parameters was studied by stepwise multiple linear regression analysis. The frequency of sister chromatid exchanges appeared to be influenced by smoking history (p less than 0.05) and season of sampling (p less than 0.01) and, if season was excluded, by age (p less than 0.05) and current smoking (p less than 0.05). The number of cells with chromosomal aberrations increased with age (p less than 0.05) and lymphocyte count (p less than 0.05), whereas the frequency of stable rearrangements was negatively correlated with current smoking (p less than 0.01).