A long-term study was performed on the effects of fluphenazine decanoate and the results were compared with those of fluphenazine-2HCl and fluphenazine enanthate. These agents given orally were equipotent in inhibiting the motility of mice. With subcutaneous administration, decanoate and enanthate showed a clearly prolonged action, whereas fluphenazine-2HCl was effective for only 3 days. Decanoate and enanthate did not produce marked hypothermia in rats. Like enanthate, decanoate inhibited, for a long duration, apomorphine-induced stereotyped behavior and methamphetamine group toxicity in mice, as well as induced catalepsy in rats. It was found that fluphenazine-2HCl markedly inhibited certain agonists-induced contraction of isolated preparations while enanthate and decanoate inhibited these contractions almost equally. In rats, enanthate induced a persistent hypotension and marked changes in ECG while decanoate showed a transient hypotension and slight changes in ECG. In the study of rat brain catecholamine turnover, these three drugs significantly increased dopamine turnover, and decanoate and enanthate were found to have prolonged effects. No significant change in noradrenaline turnover was observed. These results indicate that fluphenazine decanoate has the same spectrum of activity as enanthate except for its slower onset, weaker potency and longer duration of action. A prolonged tranquilizing effect was most evident.