Relationships among stream surface water (9-km reach), substream hyporheic water (10-m pool-riffle-pool reach), and riparian groundwater (single site) biogeochemical patterns were examined in four seasons (1989-1990) in a temperate stream exosystem (Michigan, USA). Surface water concentrations of chloride, dissolved organic carbon (DOC), and chlorophyll-a exceeded those of groundwater during most sampling periods. Groundwater and hyporheic concentrations of silica (SiO2), soluble reactive phosphorus (SRP), nitrate+nitrite (NO3-N), and ammonium (NH4-N) were generally higher than in surface water, particularly during summer. Hyporheic temperatures exhibited sharpest gradients with depth and distance downstream beneath a study riffle during summer and winter. Biologically reactive solutes (SRP, NO3-N, NH4-N, and DOC) generally decreased with depth and increased with distance beneath the riffle during summer and winter as well. Hyporheic patterns were indistinct or more variable during spring and fall and were attributed, in part, to the breakdown of thermal gradients within the bed, similar to seasonal lake turnover (mixis). Similarities between longitudinal/depth gradients in hyporheic patterns and longitudinal stream channel patterns for SiO2 and Cl (the more conservative solutes) indicated potential cumulative groundwater discharge effects through successive hyporheic zones over stream distance. Relationships between hyporheic patterns, stream channel patterns, and the biologically reactive solutes (SRP, NO3-N, NH4-N, DOC) were less clear because of potential biotic or abiotic uptake at the sediment-water interface. Groundwater-surface water interaction within a hyporheic zone forms a complex system structured not only by hydrologic forces but also by seasonal changes in temperature and discharge.