Lumbar cerebrospinal fluid (CSF) homovanillic acid (HVA), 3-methoxy-4-hydroxyphenylglycol (MHPG), 5-hydroxyindoleacetic acid (5-HIAA), cyclic AMP (cAMP) and cyclic GMP (cGMP) were measured in chronic schizophrenics with tardive dyskinesia before and three weeks after the initial treatment with sodium valproate (VPA), cyproheptadine, oxypertine or hydroxyzine pamoate. HVA levels significantly decreased after the administration of VPA, cyproheptadine or oxypertine. Cyclic GMP levels significantly increased after the administration of VPA or cyproheptadine. Elevation of the cAMP level was observed after the administration of VPA, cyproheptadine or oxypertine. An elevation of the MHPG level was observed during oxypertine treatment and a reduction of the 5-HIAA level was observed during hydroxyzine pamoate treatment. Decreases in HVA and increases in cGMP levels during treatment might be indicative of normalization of the dopaminergic-cholinergic imbalance in the brain. Lumbar CSF HVA and gamma-aminobutyric acid (GABA) were also measured in patients with tardive dyskinesia before and eight weeks after Ca-hopantenate treatment. No significant changes were observed before or after this treatment. The hypothesis is discussed that the pathogenesis of tardive dyskinesia may involve functional disorders not only of the dopaminergic or cholinergic system but also of the norepinephrinergic, serotoninergic and GABA-ergic systems.