Hematological and biochemical parameters were evaluated in 31 patients receiving 150 MBq 89Strontium (89Sr) intravenously due to painful skeletal metastases from hormone resistant prostate cancer. Two and 3 months after the injection prostate specific antigen (PSA) had increased by a median of 36% and 100%, respectively, as compared to the pretreatment value whereas alkaline phosphatase (APHOS) had decreased by about 20% (median). The leucocyte and platelet counts were reduced by about 20-35%, without reaching grade greater than or equal to 2 toxicity. Pain relief was reported in 14 of 29 evaluable patients at 2 months and in 11 of 23 patients at 3 months. It is concluded that 89Sr represents a worthwhile therapeutic modality in the palliation treatment of patients with hormone resistant prostate cancer, though the biological significance of frequently increasing PSA and decreasing APHOS is not yet completely understood.