It has been demonstrated experimentally that tolerance to the effects of lysergic acid diethylamide (LSD-25) develops rapidly, both in man1,4,6and in animals.5Tolerance to mescaline, with a less rapid development, was observed in rats by Freedman et al.5We are not aware of studies on tolerance to 2-bromo-d-lysergic acid diethylamide (BOL-148). Tachyphylaxis to LSD-25, it seems, is another...