ABSTRACT Gynogenetic diploid axolotls were produced by activating eggs with ultraviolet-inactivated sperm, and then subjecting the activated eggs to heat shock. Optimal conditions for ultraviolet inactivation of the sperm, and for suppression of the second meiotic division by heat shock, were established. Gynogenetic diploids produced by these procedures included progeny homozygous for recessive alleles carried by a heterozygous mother. Gynogenesis could, therefore, be used to uncover new mutations more rapidly than by conventional inbreeding techniques. However, some difficulty was encountered in recognizing mutant phenotypes because of the high incidence of abnormalities and deaths. Defective embryos probably resulted from a combination of heat-shock-induced damage to the eggs and the expression of deleterious recessive alleles carried by the mother.