Drosophila melanogaster, maintained on culture media containing alpha-methyl-p-tyrosine (alpha-MT) at millimolar levels for 7 days, fail to produce viable progeny. Lesser concentrations delay development. This effect of alpha-MT, an inhibitor of tyrosine hydroxylase (TH), is partially reversible by co-administration of L-dihydroxyphenylalanine, the product of TH. Potent inhibitors of other steps in the pathway for catecholamine biosynthesis are inactive except for a partial effect with dopamine B-hydroxylase inhibition. the effect of alpha-MT is due to a combination of ovulation suppression coupled with decreases in embryonic and larval viability. Effects similar to those of alpha-MT are found with millimolar levels of reserpine, prazosin and to a lesser extent, rauwolscine. No significant effects are found with propranolol, chlorpromazine, sulpiride and SK&F 83566. Mutant alleles of the gene coding for TH are known to be lethal at the embryonic stage when homozygous in both Drosophila and mice. Taken together, these results indicate that in addition to their established roles in the nervous system catecholamines function in animal development via an action mediated through alpha-adrenoceptors.