The embryonic stem cell line, S25, is a genetically modified line that allows lineage selection of neural cells (M. Li, L. Lovell-Badge, A. Smith (1998) Current Biology 8: 971-974). Here, the growth parameters of this cell line were analysed. Serial passaging in adherent conditions enabled these cells to grow rapidly (average specific growth rates of 0.035 h(-1)) and generate high viable cell densities (above 90%). The aggregation of the S25 cells into embryoid bodies (EBs) was also studied, indicating limited cell growth (maximum cell densities of 2.7 x 10(5) cells ml(-1)) and a high variability of aggregate size (70-400 mum after 8 d). Enzymatic dissociation of EBs with 1% (v/v) trypsin gave highest cell viability (91%) and density (1.4 x 10(4) cells ml(-1)) and the cells thus obtained are able to differentiate into neurons.