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Summary: A study was made of the water chemistry, tissue nutrients and surface phosphatase activities of the 2-cm apices of three mosses in four upland streams in northern England, UK. This was part of a project to optimize methods for assessing nutrient fractions in environments with highly variable water chemistry. Aqueous N and P fractions showed the greatest variability followed by moss phosphatase activities, with nutrient composition of the shoot apices the least variable. There was no consistent pattern as to which aqueous N or P fraction was the most variable. The ratio between total inorganic N and total filtrable P ranged over three orders of magnitude in some streams. The interrelations between tissue N and P concentrations, tissue N:P ratio, phosphatase activities and aqueous variables showed: [(1)] Significant +ve relationship between tissue N and aqueous NO3–N in some populations, but not between tissue P and aqueous P concentration; [(2)] Significant +ve relationships between phosphatase activities and aqueous organic N, but none with aqueous organic P; [(3)] Significant +ve relationships between phosphodiesterase:phosphomonoesterase activities and aqueous organic N; [(4)] Significant −ve relationships between phosphatase activities and tissue P concentration; [(5)] Significant +ve relationships between phosphatase activities and tissue N:P. Both types of biological measurement are valuable for monitoring ambient nutrients in upland streams. Neither is clearly better than the other, so both should be included in surveys. [Copyright &y& Elsevier]