Nitromethane (NM) and 2-nitropropane (2-NP) and versatile compounds employed in a wide variety of industrial applications, thus providing ample opportunity for occupational exposure. The purpose of this study was to determine the subchronic inhalation toxicity of NM and 2-NP in order to recommend acceptable exposure levels in the workplace. Fifty male rats and 15 male rabbits were exposed to either 98 ppm or 745 ppm of NM or 27 or 207 ppm of 2-NP 7 hours/day, 5 days/week, for periods up to 24 weeks. Fifty rats and 15 rabbits were exposed to filtered air for similar lengths of time and served as controls. Ten rats from each exposure and control group were sacrificed following 2 days, 10 days, 1 month, 3 months, and 6 months of exposure. Five rabbits from each exposure or control group were sacrificed at 1, 3, and 6 months of exposure. Effects relatable to exposure to NM were decreased body weight gain in rats following 8 weeks of exposure to 745 ppm, and a thyroid effect evidenced by an increased thyroid weight and decreased serum thyroxin levels, most notable in rabbits. Liver weights were significantly elevated in rats exposed to 207 ppm of 2-NP for 1, 3, and 6 months. No exposure-related gross or microscopic alterations were seen in any of the tissues examined for rats and rabbits exposed to 745 and 98 ppm of NM and 27 ppm of 2-NP or in tissues of rabbits exposed to 207 ppm of 2-NP. Liver neoplasms were seen in all 10 rats killed following 6 months of exposure to 207 ppm of 2-NP, indicating that 2-NP is a potent carcinogen in the rat.