In April 1967, Mount and Stephan published results of two life-cycle tests using the fathead minnow and introduced the terms 'Maximum Acceptable Toxicant Concentration' (MATC) and 'Laboratory Fish Production Index'. Life-cycle tests can now be conducted with a variety of fishes and invertebrates. The purpose of the paper is to present rationale to answer three questions: Is it better to calculate results by considering data for a smorgasbord of individual biological measurements or for one or a few integrated effects that are commercially, recreationally, or ecologically important; Is it better to calculate results using hypothesis testing or regression analysis; What terminology is appropriate for expressing results of chronic tests. The usefulness of various tests for predicting the results of life-cylce tests cannot be adequately assessed until some of these issues are resolved.