An analytical method was developed for the determination of nine antiviral drugs (acyclovir, abacavir, lamivudine, nevirapine oseltamivir, penciclovir, ribavirin, stavudine, zidovudine) and one active metabolite (oseltamivir carboxylate) in raw and treated wastewater as well as in surface water using LC/ESI tandem MS detection. Relative recoveries exceeded 80% and limits of quantification ranged between 0.2 and 10 ng L(-1). Matrix effects were compensated by the use of stable isotope labeled surrogate standards and optimized chromatographic separation on a Hydro-RP column. All antiviral drugs, except ribavirin, were detected in raw wastewater. A significant reduction in concentrations was observed for acyclovir, lamivudine, and abacavir in treated wastewater indicating a substantial removal, while nevirapine, zidovudine and oseltamivir were found in similar concentrations in raw and treated wastewater. Concentrations in river waters were in the lower ng L(-1)-range, with a maximum of 190 and 170 ng L(-1) for acyclovir and zidovudine, respectively in the Hessian Ried. Estimated total compound loads in the Ruhr river ranged between <0.1 and 16.5 g d(-1) while for the Rhine river values between 370 and 1800 g d(-1) were determined. The ratios of oseltamivir to oseltamivir carboxylate were approximately a factor of 10 higher for the Rhine than for the other rivers and streams indicating a significant contribution from other sources such as discharges from manufacturing facilities.