The generation of nitric oxide (NO) in Taxus cuspidata in immobilized support matrices and the potential role of NO as signal molecular in regulation of Taxol production were investigated. It was found that the immobilization induced a spatial and temporal-dependent NO burst in immobilized supported matrices. NO level reached the maximum in the central zone of immobilized supported matrices on day 20, which was more than twice compared with that in suspended cells. Further investigations showed that the phenylalanine ammonialyase (PAL) activity and Taxol production of the 20-day-old immobilized T. cuspidata cells increased by onefold and 11% after 4h treatment with 20 microM NO donor (sodium nitroprusside), respectively. NO inhibitor N(omega)-nitro-L-arginine and NO scavenger 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxyde partially blocked PAL activity and Taxol accumulation in immobilized cells. These results suggest that NO plays a signal role in regulation of PAL activity and Taxol production in immobilized T. cuspidata cells.