Cytokines are essential molecules throughout the development of the nervous system and also play an important role during the adult life span. In the present work, we analyzed in vitro the effect of spleen-cell-conditioned medium (SCM) on the survival and [<sup>3</sup>H]-choline uptake of neonatal rat retinal cells. SCM induced an increase in neuronal survival, glial cell proliferation and neurite outgrowth, as evaluated by biochemical and morphological criteria. These effects were time dependent; after 120 h, SCM induced a 6-fold increase in the total protein level. The effect of SCM was blocked both by the inhibition of protein tyrosine kinase activity (10 μ M genistein) and by the inhibition of cell division (20 μ M fluorodeoxyuridine). SCM also increased the uptake of [<sup>3</sup>H]-choline by retinal cells. The effect was time dependent. The maximum effect was obtained after 48 h and was maintained at a high level until 120 h. Treatment by 10 μ M genistein and 15 μ M bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA-AM) (an intracellular calcium chelator) completely blocked this effect. However, 20 μ M fluorodeoxyuridine did not abolish it. Conditioned medium obtained from glial cells stimulated with SCM (S-GCM) induced an effect on [<sup>3</sup>H]-choline uptake earlier than that promoted by SCM. Anti-interleukin-2 (IL-2) antibodies blocked the effect of both SCM and S-GCM on [<sup>3</sup>H]-choline uptake after 48 and 72 h. IL-2 (50 U/ml) elicited the same effect as that observed when the cells were maintained in the presence of SCM. Taken together, our results suggest that IL-2 plays an important role in controlling the survival and differentiation of retinal cells in vitro.