A randomized, double-blind design, with two groups and fixed sample size. The 551 participants were randomized in a stratified double-blind manner to either chlorthalidone or matching placebo in a ratio of 4:l. Subjects failing to reach goal blood pressure were randomized a second time to receive one of the following drugs in addition to chlorthalidone: reserpine, hydralazine, and metoprolol. Subjects on placebo in Step I who did not achieve goal had a corresponding Step II placebo added to their regimen.