Earlier work on the factors influencing inhibition of activation of the spermatozoa of Salmo gairdnerii has been confirmed. Diluents containing K+ and of pH less than 7.8 do not activate the spermatozoa. The presence of Na+ in the diluent has a mildly antagonistic effect on this inhibition. It has now been demonstrated that both Ca2+ and Mg2+ markedly antagonize the inhibition due to low pH and K-. It is suggested that inhibition due to potassium salts could account for the inhibition previously attributed to Androgamone I.