The current study was designed to compare the efficacy of total parenteral nutrition (TPN), provided either before or after tumor removal, in replenishing protein stores in the malnourished tumor-bearing (TB) host. Fisher 344 rats bearing a transplantable methylcholanthrene(MCA)-induced sarcoma were used. After the animals were cachectic from their tumor, a central venous catheter was inserted. At the time of catheter insertion, the animals were randomized into two groups. Group I rats had the TB hindlimb amputated whereas Group I1 rats had the nontumor bearing (NTB) hindlimb amputated. After amputation, all animals were given TPN for 10 days then sacrificed. The results demonstrated that T B rats (Group 11) had a significantly decreased tumor-free carcass weight in contrast to nontumor bearing rats (Group I). Furthermore, the TB animals had a significantly increased body weight gain after completion of TPN. This difference in body weight proved to be due almost entirely to the weight of the growing tumor. Compositional analysis revealed a significantly decreased protein stores and significantly increased fat stores of both the carcass and liver of the T B animals compared to those which the tumor had been resected. The results of the data suggest that TPN given to the sarcomabearing animal after tumor removal is better utilized for replenishing protein stores than when it is provided before removal of the tumor.