The chemiluminescence technique has been used to measure the growth of stratospheric nitric oxide from before sunrise until about 2 h prior to local noon at a constant altitude of 26.5 km at 33.1 °N. The instrument has sufficient time resolution to record the rapid growth of NO due to photolysis of NO2 during ultraviolet sunrise. As well, NO was observed to increase slowly throughout the remainder of the experiment. This slow growth is tentatively assigned to the release of NO2 and NO3 and subsequently NO from the photolysis of N2O5 formed during the night. A time dependent computer simulation of diurnal measurements is used to investigate the sensitivity of the computed NO growth curves to O3, total NOx, and the photolysis coefficient of N2O5.