The objective of the present investigation was to study the influence of the occupational nickel exposure on the concentration of nickel in nasal mucosa, plasma and urine. Plasma, urine and biopsy specimens of nasal mucosa from 318 nickel workers, 15 retired nickel workers and 57 non-exposed controls were analyzed for nickel by atomic absorption spectrometry. The results showed that nickel exposure led significantly to raised nickel concentration in nasal mucosa, plasma and urine both in active and retired nickel workers. The average nickel concentration in the nasal mucosa was highest in workers exposed to the highest atmospheric nickel concentration, inhaled as nickel subsulphide and oxide dust. Workers exposed to aerosols of nickel chloride and sulphate at a lower atmospheric nickel concentration had, on the other hand, the highest mean nickel concentration in plasma and urine. The mucosal, plasma and urine nickel concentration were significantly correlated to duration of nickel exposure. The accumulated nickel in the nasal mucosa was retained for years after termination of the nickel exposure, and slowly released with an estimated half-life of 3.5 years.