To analyze the environmental fate and migration of pesticides applied to croplands as they are affected by conservation tillage practices, pesticide models for leaching, surface water and ground water were selected and an application method was developed. Fourteen different pesticides applied to corn and soybeans were analyzed to determine probable concentrations in ground water and surface water under conventional tillage, reduced tillage and no tillage practices; the Lake Erie Basin was the study site. Surface runoff loadings and concentrations decreased under the conservation tillage scenarios, but ground water loadings and concentrations increased as a result of the decreased runoff and increased ground water recharge. Reduced tillage decreased surface runoff loads and concentrations by about 50% as compared with conventional tillage, and no tillage resulted in another 20% reduction. The pesticides with the highest surface runoff loads and concentrations were those with K sub oc values generally less than 200 ml g-1 and root zone half-lives greater than 40 d. (Copyright (c) 1987 SETAC.)