The testing of a priori contrasts, post hoc contrasts, and experimental error rates are discussed. Methods for controlling the experimental error rate for a set of a priori contrasts tested simultaneously have been developed by Dunnett, Dunn, Sidak, and Krishnaiah. Each of these methods is discussed and contrasted as to applicability, power, and availability of tables. A strategy is suggested as to how these might be employed when a researcher desires to control the experimental error rate for a set of a priori contrasts. (Author/GDC)