Statistical procedures for evaluating periphyton sampling techniques and results are described. The sampling technique utilized was glass slides incubated at various locations in a reservoir receiving industrial effluent. The density, diversity, and dominance of organisms were utilized as dependent variables. Initially, the sampling and processing technique was evaluated to determine the variability at each step. From this information, decisions were made regarding where in the process replication would be most important. Further, statistical procedures are demonstrated for relating sampling replication to the ability to detect differences between results obtained at different sampling locations. Techniques for relating processing or counting effort to the reliability of estimates of dominant species are discussed. The statistical techniques illustrated can be used to relate overall sampling or processing effort or costs to the reliability of the final results.