Parathyroid hormone 1–34 [PTH(1–34)] was shown to increase transforming growth factor β1 (TGF‐β1) and TGF‐β2 concentrations in supernatants of cultured human osteoblasts and to increase TGF‐β1 and TGF‐β2 messenger RNA (mRNA) concentrations and gene transcription in these cells. Because PTH(1–34) activates both protein kinase C (PKC) and protein kinase A (PKA) pathways in osteoblasts, we investigated the role of each kinase pathway in activation of TGF‐β3 isoforms. PTH(29–32), which activates the PKC pathway in rat osteoblasts, increased TGF‐β1 but not TGF‐β2 concentrations in supernatants of osteoblasts. Phorbol myristate acetate (PMA), a PKC agonist, increased TGF‐β1 but not TGF‐β2 concentrations. Specific PKC antagonists safingol and Gö6976 attenuated PTH(1–34)‐mediated increases in TGF‐β1 but not TGF‐β2 synthesis. PTH(1–31), which increases PKA activity in several cell culture systems, increased TGF‐β2 but not TGF‐β1 concentrations in human osteoblast supernatants. Forskolin, a PKA agonist, increased TGF‐β2 but not TGF‐β1 concentrations in supernatants of human osteoblasts. The PKA antagonist H‐89 blunted PTH(1–34)‐mediated increases in TGF‐β2 but not TGF‐β1 synthesis. Our results are consistent with the concept that PTH increases TGF‐β1 expression and secretion by pathways that involve the PKC pathway, whereas it increases TGF‐β2 expression and secretion via the PKA pathway. (J Bone Miner Res 2000;15:879–884)