The behavioral and electroencephalographic (EEG) effects of intramuscular fluphenazine decanoate (Fl-D) were investigated in rats and compared with those of fluphenazine enanthate (Fl-E) and fluphenazine HCl (Fl-HCl). It was clearly observed that 1) these two depot type neuroleptics reduced open-field activity, 2) antagonized methamphetamine-induced hyperactivity, 3) inhibited the conditioned avoidance response, and 4) produced catalepsy, for a substantially long period of time (4-35 d). Although both Fl-D and Fl-E significantly inhibited muricide in olfactory bulbectomized rats and impaired rotarod performance, these effects were relatively weak in potency and short-lasting (4 h-2 d). The EEG was changed to a drowsy pattern which consisted of high voltage slow waves following the injection of Fl-D and Fl-E. Fl-D significantly inhibited the EEG arousal response to auditory stimulation, but Fl-E did not. However, neither Fl-D nor Fl-E inhibited the EEG arousal response to electrical stimulation of the midbrain reticular formation and posterior hypothalamus. These results indicate that Fl-D has the same spectrum of pharmacological activity as Fl-E, except for its longer duration of action in antagonizing methamphetamine as well as in inhibiting the EEG arousal response to auditory stimulation.