ABSTRACT: Of importance in the design and application of improved or new modalities of treatment are their evaluation on relevant animal models. In the case of prostate cancer (PCa) the Dunning R-3327 rat prostate adenocarcinoma (PCa), and its variant sublines, is one such experimental tumor model of its human counterpart. In a preliminary study, the effect of transfer factor (TF), one form of passive immunotherapy, on tumor-associated immunity (TAD and tumour growth and histology of the G subline (a poorly differentiated, fast-growing, androgen sensitive, and poorly metastatic tumour of the Dunning R-3327 rat PCa) has been evaluated. TF prepared from the leukocytes of tumor-bearing animals and nontumor-bearing animals referred to as sensitized (STF) and unsensitized (UTF), respectively, had no significant effect on TAI or tumor size. The only noticeable effect of TF in this study was the presence of variable and moderate lymphocytic infiltrates, necrosis, and degenerative-type cells in tumors of animal recipients of STF. The failure to observe significant differences in TAI among tumor bearing and nontumor bearing animals raises doubt in part, of the immunogenicity of the G subline tumor and its appropriateness, at least for subsequent immunological studies. Further factors considered in this regard, are questions of tumor load, including the possible need for the use of adjuvant, and the parameters and sensitivity of immune responsiveness selected for evaluation and immunocompetency. Subsequent evaluation of the effect of TF on other more immunogenic variant sublines of the Dunning R-3327 rat tumor may yet provide further and more useful information.