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In autumn 1998 stream metabolism was measured in the Arizona, a Sonoran Desert stream, using single-station diel oxygen curves and all oxygen was balance model. Oxygen consumption rates of para. fluvial and channel sediments were determined with respiration chamber,. Bedload of channel sediments (sand) prevented significant primary production by benthic autotrophs, despite favorable nutrient, light, and temperature conditions. Ecosystem respiration was relatively low (1.50 g O-2 m(-2)d(-1)) and presumably fueled by production ill the riparian zone and riverine marshes. Respiration rates in the parafluvial zone and in channel sediments ranged from 0.6 to 1.4 g O-2 m(-3) sediment h(-1). Sediment organic matter (ash-free dry mass) was 4.0 +/- 1.8 kg m(-3) sediment and did not significantly differ between the channel and the parafluvial zone. Results indicate that heterotrophic processes may dominate the metabolism of desert stream segments over extended periods of time if unstable sandy bed sediments prevail.