Nickel analyses were performed by electrothermal atomic absorption spectrometry upon urine specimens obtained from electroplating workers at the beginning, middle and end of the work-shift. The means (+/- S.D.) for nickel concentrations in urine specimens from seven electroplating workers on three regular workdays were: 34 +/- 32 micrograms/L (pre-shift); 64 +/- 63 micrograms/L (mid-shift) and 46 +/- 32 micrograms/L (end-shift), compared to 2.7 +/- 1.6 micrograms/L (pre-shift) in 19 controls (hospital workers). Nickel concentrations in urine specimens from six electroplating workers on the first workday after a two-week vactation averaged: 5 +/- 3 micrograms/L (pre-shift); 9 +/- 6 micrograms/L (mid-shift), and 12 +/- 6 micrograms/L (end-shift). Nickel concentrations in personal air samples (seven hours) collected from the breathing zones of five electroplating workers on three regular workdays averaging 9.3 +/- 4.4 micrograms/m3. Nickel concentrations in the air samples were correlated with nickel concentrations in end-shift urine specimens (corr. coef. = 0.70; P less than 0.05), but were not correlated with nickel concentrations in pre-shift or mid-shift urine specimens. In view of the fluctuations of urine nickel concentrations that occur during the work-shift, the authors recommend that nickel analyses of eight hour urine specimens be used routinely to monitor occupational exposures to nickel. In situations where timed urine collections are impractical, analyses of end-shift urine specimens are the best alternative.