Aim: To assess whether osteoblast proliferation induced by hydroxyapatite (Ha) may be regulated by prostaglandin E₂ (PGE₂) and nitric oxide (NO) in a synergic fashion. Materials and methods: Human osteoblasts (HOS cell line) were cultured onto Ha with or without nimesulide, a cyclooxygenase-2 (COX-2), and/or L-NIO, an endothelial nitric oxide synthase (eNOS) inhibitor. The cells pretreated with nimesulide and/or L-NIO were cultured onto Ha added with PGE₂ and/or S-nitroso acetyl penicillamine (SNAP), a NO donor. The Ha-plated cell cultures were also added with anti-PGE₂ and/or carboxy PTIO, a NO scavenger. The cell proliferation was assessed colorimetrically from the 3-day cultures. The levels of PGE₂ and NO were determined from the culture supernatants. Results: Hydroxyapatite-induced cell proliferation was partially inhibited by nimesulide or L-NIO but fully by both inhibitors. The production of PGE₂ from the same cell cultures was inhibited fully by nimesulide but partially by L-NIO. In contrast, NO production was inhibited only by L-NIO. Partial suppression of Ha-stimulated cell proliferation by nimesulide or L-NIO was abolished by PGE₂ or NO, respectively. The combination of PGE₂ and NO donor could abrogate fully nimesulide—but partially L-NIO-mediated suppression of Ha-induced cell proliferation. Anti-PGE₂ or carboxy PTIO partially inhibited but combination of both scavengers fully suppressed the Ha-induced cell proliferation. Conclusion: Osteoblast proliferation induced by Ha may be regulated by a synergic function of PGE₂ and NO in an autocrine fashion. Clinical significance: The successful or failing Ha-based dental implantation may be determined by the synergic regulatory functions of the host PGE₂ and NO at the implanted sites.