Streams in the McMurdo Dry Valleys, Antarctica, flow during the short summer melt season (4-12 weeks) when air temperatures are close to the freezing point of water. Because of the extreme low precipitation rates, streams originate from glacial meltwater and flow to closed-basin lakes located on the valley floor. Water samples have been collected from the streams in the dry valleys since the start of the MCM LTER in 1993 and these have been analyzed for major ion and nutrient chemistry. The chemistry of the streams varies by location. Multiple controls such as landscape position, slope and morphology of the channels, and both biotic and abiotic in-stream processes, all influence the stream chemistry. Solute concentrations tend to be higher in the longer streams and sea-salt derived ions tend to be higher in streams that are closer to the ocean. Chemical weathering is an important process influencing stream chemistry throughout the dry valleys. The dominant cation in the dry valley streams is calcium and alkalinity is the dominant anion on an equivalent basis.