Seven psychotic inpatients (two women and five men) aged between 18 and 74 years, treated with neuroleptic and antiparkinson drugs, participated in a double-blind study with 1/3 DDD (Defined Daily Dose) of procyclidine, orphenadrine, or trihexyphenidyl hydrochloride against placebo. Euphoric effects were scored on a self-rating scale and extrapyramidal side-effects on the Simpson-Angus rating scale at drug administration and 1, 3 and 6 h thereafter. With regard to euphoric effect, there was a significant (P less than 0.02) difference between start and end point (0 and 6 h) for placebo but not for the active antiparkinson drugs. There was no significant difference in extrapyramidal side-effects. No preference of drug was found, and it was not possible to recognize the patient's own drug among the tested drugs. Side-effects from the antiparkinson drugs were also measured prior to the administration. Five patients did not return to their earlier antiparkinson drugs after the study.