We have measured neurofilament protein expression in cultures of human dorsal root ganglia (DRG) grown in both the presence and absence of nerve growth factor (NGF). Cultures established from DRG of 8-13 weeks gestation contained populations of both NGF-dependent and -independent neurofilament-positive cells. A recently described kinase inhibitor named K-252a inhibited NGF-dependent increases in neurofilament protein expression with half-maximal and maximal inhibition apparent at concentrations of 6 and 25 nM. At up to 50 nM, K-252a had no effect on neurofilament protein expression from NGF-independent neurons.