Previous work has shown that pig lung, among a number of tissues examined, contained relatively high amounts of survival-promoting and choline acetyltransferase (ChAT)-sustaining activities for parasympathetic, ciliary ganglion neurons from chicken embryos. It is reported here that these two activities have been partially purified and shown to coelute from several chromatographic columns, indicating that the activities probably reside in the same molecule. Three species were detected with apparent molecular weights (MW) of over 100 kDa, 40 kDa, and 3 kDa, and the two high-MW species converted into the low-MW species. The high-MW species were associated with neuritic outgrowth, whereas the low-MW species was not. This low-MW form was found to maintain survival and ChAT activity, whose EC50s were closely correlated, and was partially purified 3400-fold. The partially purified material had an EC50 of 550 ng protein/ml, and was heat-stable. It was resistant to deoxyribonucleases, ribonucleases, proteases, and neuraminidase. As previously found with the crude fraction of pig lung, the trophic effects were specific for parasympathetic neurons; neither sympathetic nor peripheral sensory neurons were affected. These findings indicate that the pig lung factor(s) has a more specific target spectrum than previously reported ciliary neuron survival factors, suggesting that it may be a novel and important neurotrophic substance.