Abstract Cells dissociated from neural retina (NR) of 8-day-old chick embryos transdifferentiated into lens and pigment cells under conditions of stationary culture (spreading culture, SpC), whereas such an alteration in the pathways of differentiation did not occur under conditions of aggregate culture (AgC) with constant gyration for 28 days. When NR cells precultivated for longer than 10 days in SpC were transferred to AgC, extensive transdifferentiation into lens (and pigment cells) occurred in aggregates after a total of 28 days' cultivation in vitro. This was confirmed by immunofluorescent observations of histological sections of aggregates as well as by quantitative immunoelectrophoresis using specific antiserum against δ-crystallin. In 10-day SpC, the presence of δ-crystallin was not detected by immunological assay. Our results suggest that NR cells become committed or ‘transdetermined’ into lens direction before detectable expression of the lens phenotype, when cultured in SpC for 10 days.