Four groups, each consisting of 10 male and 10 female Fischer-344 rats, were exposed 6 h/day, 5 days/week, for 9 days to diisobutyl ketone (DIBK) vapor at concentrations of 905, 300, 98, or 0 (control) ppm. An additional 10 rats/sex were assigned to the 905 and 0 ppm groups and allowed two weeks recovery prior to sacrifice. Rats exposed to 905 ppm had mild ocular irritation (lacrimation) and evidence of kidney toxicity, manifested as: 1) an increase in absolute and relative (as a percentage of body weight) kidney weights, 2) an increase in urine volume (and water intake) with a concomitant decrease in urine osmolality (males only), and 3) an increase in severity of hyalin droplet nephrosis in the proximal tubules (males only). Absolute and relative liver weights were also increased in both male and female rats of the 905 and 300 ppm groups. These effects either disappeared or lessened in severity following the 2-week recovery period. Male rats exposed to 300 ppm had similar renal alterations to the males of the 905 ppm group, although the alterations were fewer in number and smaller in magnitude. Kidney weights and renal histology of the males of the 98 ppm group were similar to the control male rats, although an increase in urine volume with a decrease in urine osmolality was observed. The kidney findings in this study were not surprising because of the chemical relationship of DIBK with other aliphatic ketones (e.g., methyl isobutyl ketone, methyl isoamyl ketone) which, after repeated inhalation exposure, cause hyalin droplet nephropathy in male rats. The significance of this male rat nephrosis with regard to human exposure is unknown.