The effects of tetraphenylboron on the motility and metabolism of fowl spermatozoa at 30 C were investigated. The motility of intact fowl spermatozoa was reduced by tetraphenylboron at concentrations that had little effect on the oxygen consumption and adenosine 5'-triphosphate content of spermatozoa. The inhibition of motility was reversed by the removal of tetraphenylboron. Furthermore, the addition of tetraphenylboron improved the maintenance of spermatozoa during storage. Tetraphenylboron did not affect the motility of demembraned spermatozoa, suggesting that the locus of action of tetraphenylboron is not directly on the axoneme of fowl spermatozoa.