Previously published eye lens weight-age data from known-age Columbian black-tailed deer (Odocoileus hemionus columbianus) and Rocky Mountain mule deer (O. h. hemionus) were subjected to regression analysis following computer iteration which fitted the linear relationship 100/[AGE (months) + k] = a + b log10 LENS (milligrams). Mule deer have a significantly higher lens weight than black-tailed deer of a given age although the rate of lens growth with age does not differ between the two subspecies. Sex differences were not apparent. Although deer over 2 years old cannot be aged to the nearest year from their lens weights with 95 percent confidence, the method may provide better age estimates for deer under 1 year of age than can be obtained by other techniques. Attempts to age deer collected at Hopland, California, by examination of cementum annuli in incisors gave poor results.