This report contains the results from a program designed to standardize those emission test methods promulgated by the EPA for use in determining compliance with Federal emission standards. The approach taken has been to conduct at least a limited laboratory and field evaluation, followed by an interlaboratory collaborative test of each method. Emphasis here is placed on the collaborative testing, the results of which are presented in terms of within-laboratory, between-laboratory, and laboratory bias standard deviations. These estimates are based on single-run results, and not on the results of three consecutive runs as would be required in conducting compliance testing. A brief discussion is given of the manner in which the precision estimates are derived. Determination of method accuracy is also considered where practical. The design of each test, deficiencies in test designs, and other problems affecting the test results are discussed. An improved test design that overcomes most of the problems observed in earlier tests is described. A brief discussion of current projects and future plans is given.