HFA-134a was administered to AHA rats by snout-only inhalation for 1 h daily to assess the effects of treatment on reproduction and development. 2. In a fertility study, rats were exposed to atmospheres of 2500, 10,000 or 50,000 p.p.m. HFA-134a throughout gametogenesis, mating, pregnancy and lactation. 3. In a peri- and post-natal study, rats were exposed to HFA-134a from days 17 to 20 of pregnancy and days 1 to 21 post partum to atmospheres of 1800, 9900 or 64,400 p.p.m. 4. The only treatment-related effect was a slight reduction in body weight gain of males of the treated parental generation at 50,000 p.p.m. (fertility study). 5. In neither study were there any adverse effects of HFA-134a on the reproductive performance of treated animals or on the development, maturation or reproductive performance of up to two successive generations.