On the basis of experimental data obtained in Syrian hamsters, demonstrating the highly efficient suppression of experimental and spontaneous metastases of highly-metastatic sarcoma cells by the use of allogeneic normal bone-marrow cells (BMC), a clinical protocol for the suppression of lung metastases of osteogenic sarcoma was started in 1984 in the Cancer Research Center, Moscow. From this time onwards, 24 osteogenic sarcoma patients, at stages 2A and 2B were treated with a combination of radical surgery and a single transfusion of normal (non-activated) allogeneic BMC (blood-group and Rhesus compatible). The first results of this ongoing study are now presented. Metastases appeared in 11 out of the 24 patients, generally very early during the first 3-9 months after treatment and in no case after 2 years. More than 50% of the BMC-treated patients were free of lung metastases after 2 or more years of observation; 8 out of 15 are still metastasis-free after 3-4 or more years of observation following treatment. The differences in the frequency of metastasis and duration of survival without metastasis of treated patients compared with a group of 41 osteogenic sarcoma patients at stages 2A and B, treated with radical surgery only (controls) reached significant levels 12 months after treatment and thereafter. Rapid recovery of NK cytotoxic activity has been observed in nearly all successfully BMC-treated patients.