We described here that pentoxifylline (PTX), which is well known to counteract tumor necrosis factor alpha (TNF alpha)-mediated inflammatory responses, augmented TNF alpha-induced neuroblastoma cell differentiation in conjunction with growth inhibition and cell-cycle arrest in G1 phase. PTX also enhanced TNF alpha-induced down-regulation of acetylcholine-mediated [Ca2+]i mobilization in neuroblastoma cells. Furthermore, we found that addition of cAMP failed to induce neuroblastoma cell differentiation, whereas blockade of [Ca2+]i mobilization by 8-(N,N-diethyl-amino)octyl-3,4,5-trimethoxybenzoate HCl (TMB-8, 10 microM) did induce neuroblastoma cell differentiation. Taken together, these results indicated that PTX possessed a novel signal transduction, down-regulation of [Ca2+]i mobilization, to augment but not counteract TNF alpha-mediated functions.