Hydroxyapatite (HA) and apatite based biomaterials are important for bone replacement. Different apatites could be produced by substituting calcium, phosphate or hydroxyl groups, resulting in new materials with different physical, chemical and biological properties. In this work we investigate the biological compatibility of apatites modified by divalent cations in cultured mammalian cells using Balb/c 3T3 fibroblasts cell line. Modified apatites, Ca9.5M0.5(PO4)6(OH)2 (M=Fe, Zn, Cu, Co, Sr, V e Pb) and Ca10(VO4)6(OH)2 were produced and characterized by FTIR, XRD and XRF. Extracts of each metal-modified apatites (0.1mg/mL of Dulbeco Modified Eagle Medium – DMEM without serum) were obtained. Cells (3x104) were exposed for 24 h/37C to the pure extract (100%). Afterwards, the number of viable cells was determined in a hemocitometer. The number of viable cells in the absence of any extract was taking as 100%. SHA didn’t present any toxicity while phenol killed 82% of the cells. In the presence of pure extract of Fe-HA or Sr- HA an increase of 70% and 20%, respectively, in the number of relative cells was observed. On the other hand, the number of residual cells after treatment with the pure extract of Pb+2, Zn+2, Co+2, and (VO4)3- was73, 65, 48, and 21%, respectively. In conclusion, cells response was strongly dependent on the metal that substitutes calcium or phosphate. Further studies are required to better understand the biological effect of these substitutions.