Chromium-based catalysts are used for the synthesis of polyethylene, but little is known about the hazard and biomonitoring possibilities of this type of chromium for workers who may be occupationally exposed to such compounds. Therefore, the bioavailability and toxicokinetics of chromium were studied in male Wistar rats after a single intratracheal instillation (2 ml/kg body weight) of various doses (1, 5, or 25 mg/kg body weight) of the catalyst (approximately 1% chromium bound to an amorphous silica matrix), either before (CAT-Cr[III]) or after (CAT-Cr[VI]) heat treatment. The results were compared with those of equivalent amounts of two chromium salts (CrCl(3) and K(2) Cr(2) O (7). Each dose group was composed of three rats. The concentration of chromium was determined by atomic absorption spectrometry in urine (collected daily for 7 d) and in plasma, erythrocytes, lung, and liver tissue obtained 2 d (only highest concentration) and 7 d after dosing. On d 2, a significant increase in lung weight was found in the animals treated with the highest dose of the hexavalent Cr products. On d 7, on the basis of body weights, lung weights, and lung histology, there was no overt toxicity, except after the highest dose of CAT-Cr(VI). The elimination of all forms of chromium was apparently monoexponential, with calculated half-life elimination times in urine of 4-11 h for Cr(III) (CAT-Cr[III] and CrCl3 ) and 8-21 h for Cr(VI) (CAT-Cr[VI] and K(2) Cr(2) O(7). On d 2, the erythro-cytes Cr concentrations were significantly higher for the hexavalent Cr products than for the trivalent Cr products. After 7 d, the erythrocytes Cr concentrations were significantly increased above control values (3 microg/L) only in rats treated with the 2 highest doses of Cr( VI) compounds (12 and 64 microg/L for K(2) Cr(2) O(7), and 14 and 79 microg/L for CAT-Cr[VI]). The present study shows that intratracheally instilled Cr(VI) and Cr(III) have different toxicokinetic profiles and that the Cr(VI) catalyst has the same bioavailability and excretion kinetics as a water-soluble Cr(VI) salt. Exposure to chromium compounds could be monitored by measuring Cr concen-trations in urine (shortly after exposure) and in erythrocytes (also at later time points after high Cr[VI] exposure).