Rats were exposed 6 h/day over 10 days to 0.3 mg/m3 of water soluble cadmium chloride and 0.2, 1.0 and 8.0 mg/m3 of insoluble cadmium sulphide, then killed at intervals over a 3-month period for serial measurements of lung, renal and faecal cadmium. CdCl2 and high-dose CdS animals showed a transient increase in lung weight. Clearance of both compounds was biphasic. Approximately 40% of deposited material was cleared during the 10-day exposure period. For CdCl2, only 9% of the lung burden was cleared rapidly after the last exposure (half-life 1.0 days) and 47% slowly (half-life 87 days), leaving a residual lung burden of 44%. For CdS, 41% of the lung burden was cleared rapidly (half-life 1.4 days) and 40% slowly (half-life 42 days), leaving a final residue 19%. In the CdS high-dose group, the retention of CdS in the lung was greater than that in the CdS low-dose groups, indicating that clearance mechanisms may possibly have been impaired in the high-dose group by too great a lung burden. For both compounds, faecal cadmium was initially high. Renal accumulation of cadmium was substantial for CdCl2 during the exposure period and continued over the following months until it represented approximately 35% of the total cadmium cleared from the lung. For CdS, renal accumulation was only 1% of the amount cleared from the lung. The bioavailability of Cd from CdS is thus poor, the majority being cleared from the lungs and excreted in the faeces. However, the bioavailability of inhaled CdS measured as cadmium in the kidney is greater than the bioavailability of orally ingested CdS.