Growth factor and cytokine signalling in the developing nervous system has multiple effects, ranging from cell differentiation and cell survival to modulation of cell phenotype. Molecules that can regulate growth factor signalling pathways will therefore be of importance in determining the cellular response to factor stimulation. Members of a recently described gene family, the suppressor of cytokine signalling (SOCS) family, can regulate signalling events downstream of predominantly cytokine stimulation and may have important roles in the nervous system. We have examined the temporal and spatial expression of SOCS-1, SOCS-2, and SOCS-3 in the developing and adult nervous system by use of Northern analysis and in situ hybridisation. All three genes were expressed in the brain, with maximal expression from embryonic day 14 to postnatal day 8 and declining thereafter, with SOCS-2 being the most highly expressed. In situ hybridisation analysis showed that SOCS-1 and SOCS-3 had a low and widespread pattern of expression, whereas SOCS-2 expression was higher and tightly regulated. Its expression pattern indicated that SOCS-2 was expressed exclusively in neurons and that it was switched on developmentally at the time of neuronal differentiation.