Adoptive immunotherapy using spleen cells activated with Iscador was found to inhibit tumour growth significantly (P<0.001). Metastatic B16F10 tumour bearing animals treated with a single dose of spleen cells activated with Iscador (in vitro) showed 100% inhibition of tumour nodule formation on 21st day. Single injection of splenocytes isolated from mice treated with Iscador inhibited the tumour nodule formation by 93.8%. Animals treated with in vivo and in vitro activated spleen cells along with Iscador had an increase in life span of 119% and 81% respectively. Treatment of animals with low dose of Iscador after adoptive immunotherapy further augmented the life span. Animals which underwent adoptive immunotherapy showed significantly reduced lung collagen hydroxyproline (9.8 microg/mg protein) and serum sialic acid (24.61 micro/ml serum) levels compared to control tumour bearing animals with increased levels of lung hydroxyproline (26.95 microg/mg protein) and serum sialic acid levels (151.3 microg/ml serum). Serum gamma -glutamyl transpeptidase levels were found to be significantly reduced in the group of animals treated with Iscador and Iscador activated splenocytes (16.6+/-2.3 nmol P-nitroaniline released /ml serum) Group of animals treated with Iscador activated splenocytes alone also showed significantly reduced serum gamma - glutamyl transpeptidase levels (17.3+/-10 nmol P-nitroaniline released /ml serum) compared to control tumour bearing animals (91+/-12 nmol P-nitroaniline released /ml serum).