A program for the calculation of the toxicological ED50 and the slope of the dose-effect line was developed for a programmable calculator. The method employed approximated the solution described by Bliss. Experimental data were evaluated and compared to both hand calculated results and results of other computer methods. This method produced results which differed from other computer methods by less than 1%. This program provided information necessary for the test for parallelism and estimate of relative potency of 2 dose-effect lines.