Measures of body weight change were calculated and examined in relation to the life span of 68 male and 71 female Wistar rats that were maintained either in wheel-cage units or cages without wheels. The analysis revealed the following: (a) sex and wheel exercise accounted for nearly one third of the obtained variation in life span; (b) growth rate, defined as the ratio of peak body weight to growth duration, accounted for over 15% of the variance in life span unattributable to sex and exercise; (c) measures of body weight gain early in the developmental span were virtually unrelated to life span; (d) beyond 9 months of age, measures of body weight gain showed a significant positive relationship with life span. Thus, there was no evidence of a negative relationship between life span and body weight gain during early life.