Because of the observed immunostimulatory actions of a new fermented wheat germ extract--with standardized benzoquinone composition--we have investigated the eventual tumor growth- and metastasis-inhibiting effects of this preparation (Avemar) applied alone or in combination with vitamin C. Tumor models of different origin [a highly metastatic variant of the Lewis lung carcinoma (3LL-HH), B16 melanoma, a rat nephroblastoma (RWT-M) and a human colon carcinoma xenograft (HCR25)]--kept in artificially immunosuppressed mice were applied. The metastasis-inhibiting effects of the treatments have been studied both in the presence and in the absence (following surgical removal) of the transplanted primary tumors. Combined treatments with Avemar and vitamin C—administered synchronously--profoundly inhibited the metastasis formation in all the applied tumor models while, treatments with vitamin C alone did not exert such an inhibiting effect on the metastasizing process. The degree of the observed metastasis inhibition in certain models was significant, while in others--although it was meaningful--did not prove to be significant. It is noteworthy that treatment with Avemar alone in certain models exerted a more pronounced inhibiting effect on metastasis formation than the synchronous combined treatment with Avemar and vitamin C. Furthermore, if the time schedule of the combined treatment was changed (vitamin C--instead of being administered synchronously--was given one hour after the treatments with Avemar), the vitamin C rather decreased the metastasis inhibiting effect of Avemar. It should be mentioned however, that in the case of rat nephroblastoma, a different response was observed: while, in the case of synchronous combination significant inhibition of metastasis formation was observed, treatment with Avemar alone did not produce metastasis-inhibition. It is noteworthy that in this model the metastasis-inhibiting effect of the synchronous combination treatment proved to be even more pronounced if Avemar was administered in a 100 times smaller dose than its regularly applied dosage. Treatment with Avemar and vitamin C--administered in combination or separately--in the majority of experimental models (with the exception of rat nephroblastoma) did not inhibit the growth of the primary tumors. It is reasonable, therefore, to suppose that in the observed metastasis-inhibiting effect the eventual proliferation inhibiting effect of these remedies does not play an important role. According to the results of other experiments--carried out in our laboratory in parallel with those described here--Avemar proved to have a meaningful immunostimulatory effect. It might therefore be suggested that the observed metastasis-inhibiting effect of this preparation may be mainly due to its immunostimulatory properties. The possible therapeutic benefits of Avemar and Avemar plus vitamin C are also discussed.