Six-day SRCA using normal mice developed by Bogden et al. is one of the most promising methods for in vivo chemosensitivity tests. However, this method has a problem on the influence of the host reaction during six days. Therefore, we examined the tumour growth kinetics, host reaction and expression of antitumor effect on three immunosuppressive maneuvers; cyclophosphamide (EX), cyclosporin A (CSA), and total body irradiation (TBI). The tumour diameter increased until day 16 in EX and CSA-treated groups and day 10 in TBI-treated group, but the results of the histological examination showed that tumour cells were preserved in tissue on day 14 in CSA-treated group and day 6 in EX and TBI-treated groups. These results were supported by flow cytometrical analysis. The autoradiogram using 3H-TdR showed that labelling index of the tumour cells was not affected by these immunosuppressive maneuvers. From the investigation of the antitumour activity of adriamycin and mitomycin C, it was suggested that the 12-day assay was suitable if nude mice were used in SRCA, and six-day assay, if EX-treated normal mice were used. In CSA-treated group, toxicity of anticancer drugs was manifested than usual.