Raloxifene is a selective estrogen receptor modulator. The drug reduces bone loss and prevents fractures in postmenopausal women. Tacrolimus, an immunosuppressant, is used to prevent organ transplant rejection. The effect of raloxifene and tacrolimus on the osseous bone in men has not been exhaustively determined. To study the effects of raloxifene, tacrolimus as well as concurrent administration of raloxifene and tacrolimus on the osseous tissue in male rats, a preliminary assessment of the drug action on histomorphometric parameters of rat bones was made. The experiments were carried out on mature male Wistar rats. The animals were divided into six groups, 7 animals each: I--control rats; II--rats which were administered raloxifene (5 mg/kg po daily); III-- rats which were administered tacrolimus (0.3 mk/kg po daily); IV - rats which were administered tacrolimus (0.6 mg/kg po daily; V-- rats which were administered raloxifene (5 mg/kg po daily) and tacrolimus (0.3 mg/kg po daily); VI - rats which were administered raloxifene (5 mg/kg po daily) and tacrolimus (0.6 mg/kg po daily). The drugs were administered for 4 weeks. Body mass, macrometric parameters of the tibia, femur and L-4 vertebra, histomorphometric parameters of tibia (transverse growth, width of osteoid, area of the transverse cross section of bone marrow cavity and cortical bone), and the femur (width of trabeculae, width of epiphyseal cartilage) were examined. The action of raloxifene in male rats was demonstrated through increased width of osteoid. An increased traverse growth of bone and osteoid width as well as transverse cross section of the cortical bone and the marrow cavity and increased thickness of trabeculae were observed in male rats receiving tacrolimus at 0.3 mg/kg. The administration of tacrolimus at 0.6 mg/kg resulted in increased traverse growth of bone and increased thickness of osteoid, whereas the thickness of trabeculae remained unaffected. The results obtained in the rats administered concurrently raloxifene and tacrolimus (at 0.3 mg/kg or at 0.6 mg/kg) were similar to those obtained in the group of rats receiving tacrolimus at 0.3 mg/kg. It seems that the most valuable in entire experimental system of the study are the results obtained in the group receiving tacrolimus at 0.3 mg/kg po, which are indicative of intensified bone remodeling processes with dominant the bone formation process.