A photochemical box model has been used to model the measured diurnal ozone cycle in spring at Jungfraujoch in the Swiss Alps. The comparison of the modelled diurnal ozone cycle with the mean measured diurnal ozone cycle in spring, over the period 1988-1996, shows a good agreement both with regard to the shape and amplitude. Ozone concentrations increase during the daytime and reach a maximum at about 16:00-17:00 (GMT) in both the modelled and the mean observed ozone cycle, indicative of net ozone production during the daytime at Jungfraujoch in spring. The agreement is better when the modelled ozone cycle is compared with the mean measured diurnal cycle (1988-1996) filtered for north-westerly winds > 5 m/s (representative of regional background conditions at Jungfraujoch). In addition to ozone, the modelled diurnal cycle of [HO2] + [CH3O2] also shows rather good agreement with the mean diurnal cycle of the peroxy radicals measured during FREETEX '96, a FREE Tropopsheric Experiment at Jungfraujoch in April/May 1996. Furthermore, this mean diurnal cycle of the sum of the peroxy radicals measured during FREETEX '96 is used to calculate, using steady-state expressions, the respective diurnal cycle of the OH radical. The comparison of the OH diurnal cycle, calculated from the peroxy radical measurements during FREETEX '96, with the modelled one, reveals also good agreement. The net ozone production rate during the day-time is 0.27 ppbv h-1 from the model, and 0.13 ppbv h-1 from the observations during FREETEX '96. The observations and model results both suggest that the diurnal ozone variation in spring at Jungfraujoch is primarily of photochemical origin. Furthermore, the observed and modelled positive net ozone production rates imply that tropospheric in situ photochemistry contributes significantly to the observed high spring ozone values in the observed broad spring-summer ozone maximum at Jungfraujoch.