Measurements of OH, the sum of peroxy radicals (RO_x), non-methane hydrocarbons (NMHCs) and various other trace gases were made at the Meteorological Observatory Hohenpeissenberg in June 2000. The data from an intensive measurement period characterised by high solar insolation (18-21 June) are analysed. The maximum midday OH concentration ranged between 4.5 x 10⁶ molecules cm^-3 and 7.4 x 10⁶ molecules cm^-3. The maximum total RO_x mixing ratio increased from about 55 pptv on 18 June to nearly 70 pptv on 20 and 21 June. A total of 64 NMHCs, including isoprene and monoterpenes, were measured every 1 to 6 hours. The oxidation rate of the NMHCs by OH was calculated and reached a total of over 14 x 10⁶ molecules cm^-3  s^-1  on two days. A simple photostationary state balance model was used to simulate the ambient OH and RO_x concentrations with the measured data as input. The model was able to reproduce the main features of the diurnal profiles of both OH and RO_x. The model results proved to be most sensitive to assumptions about the mixing ratio of formaldehyde (HCHO), which was included as a proxy for carbonyl compounds, and about the partitioning between HO₂ and RO₂. The measured OH concentration and RO_x mixing ratios were reproduced well by assuming the presence of 3 ppbv HCHO and a  ratio HO₂/RO₂ between 1:1 and 1:2. The most important source of OH, and conversely the greatest sink for RO_x, was the recycling of  HO₂ radicals to OH. This reaction was responsible for the recycling of more than 45 x 10⁶ molecules cm^-3  s^-1 on two days. The most important sink for OH, and the largest source of  RO_x, was the oxidation of NMHCs, in particular, of isoprene and the monoterpenes.