The soluble toxicity of 5 different hydroxylapatite granulates was tested in osteoblast cell cultures. We established a human osteoblast-like cell culture and a culture of rat (Lewis) osteoblast-like cells. The granulates were also tested in cultures of human gingival fibroblasts as a conventional system. It is demonstrated that the osteoblast-like cell cultures are of higher sensitivity than fibroblast cultures which do not show any reaction to the extracts of hydroxylapatite granulates. Only 2 hydroxylapatite granulates show some toxic. The human osteoblast-like cells reacted slightly more sensitive to toxic substances of the materials tested than rat osteoblast-like cells. It is demonstrated that the osteoblast-like cell cultures are a highly sensitive test system for materials with low toxicity.