The survival of sympathetic and sensory neurons is known to be controlled by nerve growth factor (NGF) supplied by the targets of innervation, yet little is known about how target NGF synthesis is regulated. We have investigated the pattern of NGF mRNA expression in developing rat heart ventricle using a sensitive RNA blotting procedure. We find that the concentration of NGF mRNA increases steadily from Embryonic Day 17 to peak levels at 10–14 days postnatal and then declines about twofold and stabilizes at the level found in adults. The rise in NGF mRNA concentration correlates with the arrival and differentiation of sympathetic nerve terminals in the heart and the cessation of sympathetic cell death. To assess the role of innervating sympathetic neurons in regulating NGF mRNA expression, neonatal rats were sympathectomized by treatment with 6-hydroxydopamine and heart ventricles were assayed for NGF message. Although this treatment reduced ventricle norepinephrine content by 82%, no significant change in NGF mRNA concentration was observed. These results suggest that the developmental program of NGF mRNA production in the heart is not influenced by innervating sympathetic neurons.