ABSTRACT Radioimmunoassay (RIA) and competitive protein binding (CPB) assays provide dose response curves which show severe nonlinearity and the residual (error) variance is non-uniform and not normally distributed. Accordingly, several classic “least squares” statistical procedures commonly used for bioassay data are not directly applicable. Linearization may be obtained by the use of the logit transformation, but this increases non-uniformity of variance. We have utilized an empirical quality control system in order to obtain estimates of the stability, precision and reproducibility of the radioimmunoassays and CPB assays. These methods provide sequential monitoring of the performance of the assays, and permit the determination of valid estimates of confidence limits on potency estimates.