Application software for economical and convenient calculation of median effective doses, confidence limits, potency ratios and slopes of quantal dose-response curves using a microcomputer is presented. The PASCAL language program is stored on diskette and it is compatible with many commercially available microcomputer systems. The program will simultaneously calculate the parameters for up to 20 different treatments and a total of 100 doses. Comparisons between the results of calculations of the LD50 of thiopental in mice using the PASCAL program, a modem-accessed commercially available probit analysis program and three, widely accepted manual calculation methods are made. The results of calculations of parallelism and the potency ratio between thiopental and phenobarbital-induced death in mice are shown.