The capacity of neuroblastoma cells to undergo differentiation in response to retinoids (Brown et al. 2005) is being targeted as the basis for development of novel retinoid-based therapeutic regimes for the treatment of neuroblastoma disease (Riddoch et al. 2005). Relatively little is known about the changes in expression of membrane transport proteins in neuroblastoma cells following differentiation but mapping these changes will be central to the development of novel treatments and therapies. Radiolabelled amino acid uptake (0.5μCi ml^-1, 0.1-500μM, 10min, 37°C) measurements were performed in a HEPES/Tris-buffered bicarbonate-free Krebs solution (pH 7.4) using human SH-SY5Y neuroblastoma cells grown on plastic in the presence or absence of 1μM 9 cis-retinoic acid (9cRA) for 7 days. 9cRA-induced differentiation had varying effects on uptake of a number of amino acids. Differentiation led to a decrease in [³H]taurine [from 1243 ± 74 (54) to 405 ± 37 (54) pmol mg^-1 (10min)^-1, p<0.001 unpaired two-tailed Student’s t test], [³H]proline [1046 ± 68 (21) to 558 ± 45 (21) pmol mg^-1 (10min)^-1, p<0.001] and [³H]glutamic acid [627 ± 58 (6) to 454 ± 35 (6) pmol mg^-1 (10min)^-1, p<0.05] uptake, an increase in [³H]lysine [1906 ± 131 (10) to 3756 ± 511 (10) pmol mg^-1 (10min)^-1, p<0.01] uptake but no effect on uptake of [³H]GABA [374 ± 27 (5) and 324 ± 48 (6) pmol mg^-1 (10min)^-1, p>0.05]. All data are mean ± SEM (n). In undifferentiated cells, taurine uptake has many characteristics of the TauT transporter (Ramamoorthy et al. 1994) being a high affinity (K_m 26.6 ± 3.4 μM, r² = 0.954) Na⁺ and Cl^–-dependent carrier that is inhibited by unlabelled (all 1mM) taurine, β-alanine, GABA and β-ABA but not by proline, MeAIB, α-ABA, glycine, serine and valine. Taurine uptake had similar characteristics in differentiated cells but uptake was always significantly lower (p<0.001) than in undifferentiated cells. In conclusion, 9cRA-induced differentiation of SH-SY5Y neuroblastoma cells is associated with a change in expression of the complement of amino acid transporters expressed at the plasma membrane. Differentiation of SH-SY5Y cells is also associated with altered Ca²⁺ signalling (Brown et al. 2005; Riddoch et al. 2005). The nature of the relationship between altered cell signalling and transporter function requires further investigation.