Changes in the activities of enzymes involved in the synthesis or degradation of transmitters has been used as an index of maturation in autonomic neurons. In some cases, a reduction in enzyme activity during normal development may reflect decreased cell survival rather than, or in addition to, changes in the rate of development. Similarly, changes in enzyme activity following experimental manipulation during development may also reflect cell loss. In the ciliary ganglion, biochemical indexes of development are altered after denervation, and after treatment with a ganglionic blocker, chlorisondamine. Surgical removal of afferents to the ciliary ganglion in the early chick embryo results in a virtually complete loss of ganglion cells. Chiappinelli et al. have reported that choline acetyltransferase (ChAT) is reduced in chick iris and ciliary ganglion after chronic treatment with chlorisondamine (on days 5, 8, 10 and 13 of incubation). This suggests that the development of transmitter enzymes may be regulated via interaction at the presynaptic site. Since they also report that chlorisondamine treatment reduced ganglionic dry weight, which could reflect a loss of cells, it may be that the same synaptic interaction governs cell survival as well as enzyme maturation. The present study provides evidence that treatment with chlorisondamine does, in fact, reduce cell survival in the ciliary ganglion.