Stable isotope analysis of rat tissues to determine effects of gonadectomization. Four groups - female, ovarectomized, male, and castrated male - were fed a constant diet for 30 days. Fat, muscle, liver, and kidney were sampled at the experiment's end while serum and blood were sampled at days 0, 1, and 30. We found that sex and removal of gonadal hormones are factors either individually or interactive for carbon and nitrogen stable isotope composition  in serum and blood (at day 30) as well as stable nitrogen isotope composition of muscle and liver. Furthermore, the degree of fractionation in these tissues is related to growth rate.