Groups of 50 male and 50 female B6C3F1 mice inhaled 10 or 40 ppm 1,2-dibromoethane 6 h/day, 5 days/week, for 103 (10 ppm) or 90 (40 ppm) weeks. Focal epithelial hyperplasia was found in 1 (low dose group) and 10 (high dose group) males and 3 (low dose group) and 11 (high dose group) females. Squamous papillomas or adenomas were seen in 3 males and 7 females in the high dose groups. Squamous, adeno-, or mixed carcinomas were present in 7 females in the high dose group. One poorly differentiated sarcoma and 2 hemangiosarcomas were observed in females in the low and high dose groups, respectively.