A mutation in the age-1 gene of the nematode Caenorhabditis elegans has been shown to result in a 65 percent increase in mean life-span and a 110 percent increase in maximum life-span at 25 degrees. One of the hallmarks of organismic aging and senescent processes is an exponential acceleration of age-specific mortality rate with chronological age. This exponential acceleration is under genetic control: age-1 mutant hermaphrodites show a 50 percent slower rate of acceleration of mortality with chronological age than wild-type strains. Mutant males also show a lengthening of life and a slowing of the rate of acceleration of mortality, although age-1 mutant males still have significantly shorter life-spans than do hermaphrodites of the same genotype. The slower rates of acceleration of mortality are recessive characteristics of the age-1 mutant alleles examined.