Vitamin D3 and 25-OH-D3 were tested for their effect on glycosaminoglycan (GAG) production in micro high density cultures of stage 22-24 chicken limb bud mesenchyme. Vitamin D3 (at concentration of 5 x 10(-6)M) and its biologically active metabolite, the 25-OH-D3 (at concentration of 5 x 10(-8)M) stimulated the synthesis of GAGs indicating the increase of radioactive sulfate incorporation and uronic acid content in a dose-dependent way. The findings obtained after the treatment with 25-OH-D3 are comparable with earlier studies performed on chondrocyte cultures (Corvol et al. 1978, 1980), while the results observed after the vitamin D3 treatment are the first indications that vitamin D3 can also influence the cartilage matrix composition.