Reproductive toxicity of monochlorobenzene was evaluated in CD rats (30/sex/concentration group) receiving whole-body exposure to vapor concentrations of 0, 50, 150, and 450 ppm through 2 consecutive generations (F0 and F1). F0 adults were exposed for 6 hours/day during a 10 week pre-mating treatment period. Following mating, females were exposed for 6 hours/day on gestation days 0-19, lactation days 5-21, and post- weaning until sacrifice. After mating, males continued to be treated until sacrifice. F1 pups, 29 days of age, were exposed for 11 weeks prior to mating. Exposure of F1 animals during mating, gestation, and lactation was similar to that for F0 animals. The treatment had no adverse effects with respect to mortality, body weight gain, food consumption, clinical observations, reproductive performance, or fertility of F0 and F1 adults, or well-being of F1 and F2 pups. Treatment increased relative liver weight of adult males (mid- and high-treatment levels for F0; all treatment levels for F1). F0 and F1 adults had hepatocellular hypertrophy and degenerative and inflammatory lesions in the kidney; the incidence and severity of these lesions in adult males increased with treatment level and with subsequent generations. Mid- (F1) and high-concentration males (F0 and F1) had unilateral and bilateral testicular degenerative changes.