The ejaculatory response following acute injections of p-chloroamphetamine (PCA) and several other drugs was measured by weighing the compact seminal material accumulated over 2 hr. p-Chloroamphetamine caused a dose-dependent ejaculatory response that was inhibited by the inhibitor of the synthesis of 5-hydroxytryptamine (5-HT), p-chlorophenylalanine (PCPA), neurotoxic doses of PCA, reserpine, DSP 4 a selective noradrenergic neurotoxin given 48 hr before PCA, the inhibitor of synthesis of noradrenaline (NA) FLA 63, the specific inhibitors of uptake of 5-HT, alaproclate, fluoxetine and norzimeldine and the selective inhibitor of the uptake of NA, CPP 199, the E form of norzimeldine. The doses of several receptor antagonists producing a 50% decrease in the weight of seminal material were determined. The non-selective 5-HT receptor antagonists, metitepine and methergoline, the selective alpha 1-adrenoreceptor antagonists, prazosin and phenoxybenzamine and the non-selective alpha-adrenoreceptor antagonist, phentolamine, had strong effects, followed by the selective 5-HT2 antagonists, ketanserin and pirenperone. Yohimbine, an alpha 2-adrenoreceptor antagonist and atropine, a muscarinic receptor antagonist, only produced a partial blockade. The rank order of potency for some dopamine (DA) receptor antagonists was chlorpromazine, domperidone, haloperidol, pimozide. Remoxipride, a selective DA2 receptor antagonist and the selective DA1 antagonist, Sch 23390, had no effect. The following drugs had no effect: propranolol, naloxone, picrotoxin, cimetidine and mepyramine. The 5-HT receptor agonist 5-methoxy-N,N-dimethyltryptamine (5-MeODMT 3 mg/kg, i.p.) produced a small effect on the weight of seminal material, although 72% of the rats ejaculated. d-Amphetamine did not induce ejaculation at 5 mg/kg but had a marked effect at 15 mg/kg.(ABSTRACT TRUNCATED AT 250 WORDS)