AbstractThe effects of undernutrition on the developing cerebellum were studied in 30‐day‐old rats undernourished from birth byrestricting access to the lactating mother. These animals showed a significant reduction in cerebellar weight when compared with well‐nourished controls. Quantitative studies of the cerebeller vermis revealed a 34.2% reduction in total area, with the densityof both granule cells and Purkinje cells increased. Network analysisof Golgi‐Cox preprations indicated a significant increase in the density of dendritic fields of Purkinje cells, although there was a 37% decrease in overall network size, due to reduction inthe total number of dendritic segments, and a reduction in the length of distal segments. Topological analysis indicated that the network had developed by terminal branching, as in normal animals, butwithsome deviation from the usual purely random branching pattern.All the observed modifications may be accounted for in terms of alterations in protein synthesis and DNA synthesis ocurring in undernourished animals. This leads to alterations in the extent of the intereuronal matrix, a rdduction in the number of granule cells and direct effects in Purkinje cell metabolism, all of which influence dendritic development, although the relative impotance of each of these factors awaits precise def