Growth cones were isolated from the forebrains of 1, 5 and 9 days-old rats. The ultrastructural characterization of the obtained subcellular fractions reveals that two of them (GC1 and GC2) contain predominantly growth cones. It was found that the protein content of the membranes contained in these fractions increases 7.5 times, while in whole forebrain the increase is only 3 times, showing that during the studied developmental period there is a predominant protein enrichment of the specialized brain structures (e.g. growth cones). Electrophoretic studies show that there are characteristic changes of the Coomassie Brilliant Blue R250 staining and concanavalin A reactive protein profiles. Comparison of the protein patterns of growth cones to those of synaptosomes from mature forebrain reveal a number of bands, which appear to be characteristic for one of these structures. The possible roles of the developmentally controlled proteins in the processes of synaptogenesis is discussed.