1. Some mechanisms of action of neuroleptics at cellular level are reviewed, mainly the effects on synaptic transmission and the effects on chromatin. 2. As regard to the effects at synaptic level, a brief review is presented on the available evidence in support of the currently prevailing dopamine hypothesis. 3. Studies carried out on the mechanisms and sites of action of neuroleptics on chromatin show that: a. Behavioral changes caused by psychotropic drugs in experimental animals are associated with chromatin alterations and induced macromolecular syntheses. b. Parkinsonian and possibly drug-induced extrapyramidal symptoms are associated with aberrations in protein synthesis. c. Destabilization under "stress" of the heterochromatin in schizophrenics seems to be due to histone modifications and is partly prevented by neuroleptic treatment.