PARLIN is a program for the statistical analysis of biological assays that are either completely randomized, or in randomized blocks, in which the regression on log dose is linear with a constant variance per response. An earlier program (McArthur et al., J. Pharmacol. Exp. Ther. 153: 573-580, 1966) has been completely rewritten, improved and extended in its facilities. PARLIN, written in FORTRAN IV, will handle up to 99 test preparations, up to 100 doses in all, and up to 50 responses per dose. It is designed with special attention to simplicity for routine use, versatility of facilities and output immediately available for all forms of reporting results. A wide choice of transformations of response is available. The output reproduces the data for verification and tabulates potency estimates with limits at probabilities .95, .99; optional output includes an analysis of variance, information on validity, values of residuals and a rough plot of the dose-response relation.