An immunocytochemical study was performed on the chick embryo retina to detect the changes in intermediate filament (IF) composition in correlation with development. Results showed that all three major neurofilament subunits (NF L, M and H) were expressed from very immature neurons at the same time. No delayed expression of NF-H was observed. Vimentin (VT) was also present from very early stages in both neuronal and glial cells, but it was not detectable at hatching. Its distribution changed in retinal layers throughout development. It co-existed with NF in neurons, and conversely, it preceded the appearance of the typical glial fibrillar acidic protein (GFA-P), which was detected in radial fibres of Müller cells from day 16 of incubation. These in vivo data were compared with immunocytochemical staining of retinal cultures, grown either on collagen or on polylysine. NF-L and GFA-P were not detectable in vitro. Moreover, the early expression of NF subunits was shown to be influenced by the type of substratum. The contemporary presence of vimentin and neurofilaments was clearly shown both in neuronal cell bodies and processes. The results also show that in the chick retina the pattern of composition of intermediate filaments changes with maturation. Moreover, in vitro conditions influence the expression of IF components. These data are of interest when performing in vitro analysis of the effect of exogenous substances affecting neuronal maturation and differentiation.