Vinylidene chloride (VDC) monomer dissolved in olive oil was given orally to female BD IV rats (150 mg/kg body weight) on the 17th day of gestation. Their offspring were treated weekly with 50 mg/kg body weight VDC by stomach tube from the time of weaning for life span. Liver and meningeal tumours were more frequently observed in treated than in untreated animals, but the total number of tumour-bearing animals was not significantly different between treated and untreated animals. Chloroprene (CP) monomer dissolved in olive oil was given orally to female BD IV rats (100 mg/kg body weight) on the 17th day of gestation and their offspring were treated weekly with 50 mg/kg body weight by stomach tube from the time of weaning for life span. Total incidence of tumours was similar in treated and untreated animals. The data presented provide limited evidence of the carcinogenicity of VDC and no evidence of the carcinogenicity of CP when given by the oral route to rats.