Tropospheric OH radical concentrations were observed at two locations in Germany by long-path UV absorption spectroscopy. During the summer months, noontime concentrations at sunny days averaged at 1.6¿106 OH cm-3. The highest concentrations observed so far did not exceed 2.5¿106 OH cm-3. The highest concentrations observed so far did not exceed 2.5¿106 OH cm-3. A number of possible spectral interferences by atmospheric trace gases (SO3, CH2O, CS2) were identified, and OH concentrations, as derived after correction for those interferences (if necessary), are reported for 1979 through 1981.