Past and present exposure to nickel was studied in an electrolytic nickel refinery, where an increased incidence of nasal cancer had been reported, using nickel analyses in air, blood and urine. Genotoxic effects were studied using analysis of micronuclei from acridine orange-stained smears from the buccal mucosa of the workers. Workers used respirators or masks in tasks where the exposure was expected to be high. Inside the mask, nickel concentrations were 0.9-2.4 micrograms m-3 in such tasks. In those tasks where masks were not used, nickel concentrations in the breathing zone were 1.3-21 micrograms m-3. Air-borne nickel concentrations (stationary sampling) varied between 230 and 800 micrograms m-3 in 1966-1988 with no systematic change; thereafter lower concentrations (170-460 micrograms m-3) have been observed. After-shift urinary concentrations of nickel were 0.1-2 mumol l-1; they showed no correlation with nickel concentrations in the air. Concentrations of nickel in the urine were still elevated after a 2-4 week vacation. The frequency of micronucleated epithelial cells in the buccal mucosa of nickel refinery workers was not significantly elevated by comparison with referents. No relationship was observed between micronucleus frequencies and levels of nickel in air, urine or blood.