This research investigated the effects of chronic exposure of amphibian tadpoles and acute exposure of embryos to the agricultural chemical atrazine;Tadpoles were chronically exposed from the first feeding stage through metamorphosis to three levels of atrazine. Concentrations of 30, 300 and 600 mug/L reflect exposures likely to occur in streams, wetlands and temporary waters near croplands. Cricket frogs (Acris crepitans), wood frogs (Rana sylvatica) and northern leopard frogs (R. pipiens ) were evaluated on rate of growth, days to metamorphosis, metamorphic success, and juvenile weight and length. A repeated measures ANOVA evaluated the rate of growth (increase in SVL and weight gain) over the first three weeks of exposure. Other endpoints were compared with a single factor ANOVA. There were no significant differences for R. sylvatica or R. pipiens. The most notable results are a significant (P < 0.05) increase in days to metamorphosis and decrease of post-metamorphic dry weight for A. crepitans when exposed to 300 and 600 mug/L of atrazine. Relating these results to life history characteristics suggests a reason for concern over environmental exposures. Metamorphic cricket frogs emerge from breeding waters in late summer, and they apparently reach full adult size prior to hibernating about two months later. Delayed metamorphosis and low body weight at emergence may reduce their ability to survive hibernation;The Frog Embryo Teratogenesis Assay-Xenopus (FETAX) procedure exposes South African clawed frog (Xenopus laevis) embryos for 96 hours to a range of chemical concentrations. The percentage of embryos exhibiting terata is used to estimate an effective concentration (EC50). The 96-h EC50 (terata) for pure atrazine (13.4 +/- 5.2 mg/L) was not significantly different from atrazine when in a 1:1 combination with metolachlor (14.3 +/- 2.5 mg/L), a herbicide often formulated with atrazine. Neither was there a significant difference between the EC50s for pure metolachlor (15.2 +/- 3.1 mg/L) and the 1:1 combination with atrazine (10.5 +/- 2.8 mg/L, p = 0.069). In a separate FETAX study, pure atrazine was compared to two commonly applied commercial products. There were no significant differences in estimated EC50s between pure atrazine and a 41 percent liquid or a 90 percent emulsifiable granule formulation.