Activities of acetylcholinesterase (AChE), neuropathy target esterase (NTE), and carboxylesterase (CbxE) were compared in neuroblastoma cells of human origin (SH-SY5Y) and murine origin (NB41A3). 2. Mouse neuroblastoma cells had lower specific activities of NTE and CbxE than did human neuroblastoma cells; specific activities in the murine cells correlated with specific activities in mouse brain. 3. AChE activities in mouse and human neuroblastoma cells were considerably lower than AChE activities in mouse or hen brain. 4. Inhibition of esterases did not demonstrate interspecies differences for 12 of the 17 anti-esterase compounds tested with human and mouse neuroblastoma cells.