Osteogenic protein-1 (OP-1), a member of the transforming growth factor-beta (TGF-beta) superfamily, has been demonstrated to stimulate dendrite growth from sympathetic neurons in culture. However, it is not known whether OP-1 affects dendrite growth from central nervous system neurons. Therefore we quantified axon and primary, secondary, and total dendritic growth from embryonic mouse cortical neurons (E 18) grown in vitro in a chemically defined medium. Morphology and double immunolabeling (MAP2, NF-H) were used to identify cortical dendrites and axons after 3 days in vitro. Cell morphology, neuron survival, and axon length were similar under all experimental conditions. The number of primary dendrites also was similar; however, the length of primary dendrites and the length and number of secondary dendrites were significantly increased by the addition of OP-1 to the culture medium. This increase in dendrite growth was dose-dependent; maximal dendritic growth was observed after the addition of 30-100 ng/ml of OP-1 to the culture medium. Specific support of dendrite growth was not observed when neurons were exposed to other members of the TGF-beta superfamily. These findings demonstrate that OP-1 selectively increases dendrite growth from cerebral cortical neurons in vitro.