Two crossover, placebo-controlled experiments were conducted in the present study examining the effects of mescaline on urinary catecholamine excretion. The first involved 12 psychiatric patients who received mescaline and placebo treatments in two separate sessions with a washout period of 7 days between sessions. The second involved 12 healthy, non-hospitalized patients who received mescaline and no-drug treatments in sessions that were held successively over two days. The outcomes of interest were norepinephrine, epinephrine, and vanilmandelic acid (VMA) excretion levels which were measured over a 24-hr period. Although epinephrine excretion rates were higher in the second trial, the results of both trials were consistent in showing a decline in the excretion of epinephrine during the 2- to 8-hr period when mescaline action is greatest.