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The concentrations of p-tyramine (p-TA), m-tyramine (m-TA), dopamine (DA) and their principal metabolites, p-hydroxyphenylacetic acid (p-HPAA), m-hydroxyphenylacetic acid (m-HPAA) and homovanillic acid (HVA) were determined in the corpus striatum of Swiss mice at various times after the subcutaneous administration of beta-phenylethylamine (PE) (50 mg/kg). Initially p-TA concentrations were reduced but rapid synthesis was apparent up to 2 h after PE administration. PE treatment increased m-TA and these increases reached significance at 1 and 8 h. PE caused a bimodal increase in p-HPAA and m-HPAA concentrations with the first peak observed at 0.5-1 h due to initial release of p-TA and m-TA. Rapid synthesis of p-TA and m-TA resulted in increased acid concentrations at 4 h. HVA concentrations were increased up to 1 h after PE administration. The synthesis of p-TA and m-TA is related to that of DA probably as a result of the activation of tyrosine hydroxylase. PE may serve as a precursor for p-TA synthesis when the endogenous PE concentration is greatly elevated.