A partial "double-blind" study was performed in a small series of Negro women with moderately severe hypertension to compare the effects of guanethidine sulfate and methyldopa. Both compounds are potent hypotensive agents requiring titration to achieve the exact tolerated dose in individual patients. A previously described technique for controlled assay of drugs of this nature was again applied and the results indicate that within the limits imposed by postural hypotension, the hypotensive effects were essentially the same with both preparations.