The present study is an examination of the qualitative and quantitative changes in the morphology of neurons in the inferior olivary nuclear complex ( IOC ) of the chicken. The development of the chicken IOC was studied with the Golgi technique between embryonic day 11 (E11) and posthatch day 35 ( P35 ). The olivary cells change most between E11 and E19 and are essentially mature (i.e., similar to P35 ) at E19 . These changes chiefly involve a gradual loss of features that typify immature growing cells (e.g., growth cones, growth buds, filopodia, beaded dendrites); from E11 to P35 there is an increase in the soma size by 42%, an increase in the dendritic field size by 49%, and a decrease in the number of dendritic branches by 47%. A minor but significant fall in the number of dendrites per neuron between E11 and E19 was observed, but as there is no significant difference between E11 and P35 , the relevance of this observed change, if any, is unclear. On the basis of dendritic branching, it appears that one type of olivary neuron is present in the chicken, which is similar to the type of neuron found in the caudal medial olive (MO) and the caudal dorsal olive (DO) of mammals ( Schiebel and Schiebel , '55; Rutherford and Gwyn , '80). This finding correlates with the proposal that the avian IOC corresponds mostly to the mammalian MO and DO and that only a small portion corresponds to the mammalian principal olive ( Furber , '83).