Abstract 1. 1. SH-SY5Y, an adrenergic human neuroblastoma cell line, was used to examine the hypothesis that d-lysergic acid (LSD) affects the metabolism of microtubule-associated tau protein, thus affecting microtubule assembly and the transport of neurotransmitters. 2. 2. After 48 hr treatment LSD (10 −5 and 10 −7 M) decreased 50 kDa tau protein in the membrane (pellet) fraction. The drug (10 −5 M) also decreased in the cytoplasmic (supernatant) fraction. 3. 3. This reduction in tau protein was accompanied by a 65% increase ( P < 0.05) in total protein after LSD (10 −7 M) in the cytoplasmic fraction.