The effect of hyperthermia on the spleen cells of Meth A-hyperimmunized BALB/c mice (Meth A-Im-SPL) was examined. Three kinds of heating were employed: (a) a cell suspension of Meth A-Im-SPL was directly heated for 1 h at 41 degrees C; (b) the whole body of Meth A-hyperimmunized mice was heated in the same manner--the antitumour activity of Meth A-Im-SPL was examined by Winn assay after heating; (c) the whole body of BALB/c mice intradermally inoculated with a mixture of Meth A-Im-SPL and Meth A cells (Winn assay) was heated in the same manner. The results showed that the antitumour activity of Meth A-Im-SPL was not affected by heating in vivo (Experiments B and C), although it was affected in vitro (Experiment A). Furthermore, slight augmentation of the antitumour activity of Meth A-Im-SPL was observed on heating in vivo. This shows the possibility of combination therapy involving adoptive transfer and whole-body hyperthermia.