The investigator of this study, using a sample that included 382 boys from the City of New York, 366 girls from the City, and 379 boys and 368 girls from the suburban areas of the county of Westchester, attempted to ascertain the operational, cognitive objectives of the two biology achievement instruments. The method used to analyze objectives was homogeneous keying, a method of cluster analysis. When this technique was applied to the variance-covariance matrix between the items of each test, the resulting clusters represented the desired objectives of the tests. Correlations between clusters answered questions about similarities or differences of the tests on the operational level. Based on the analysis, the following conclusions were drawn: Both the Nelson Biology Test, Form E 1965 and the New York State Regents Examination in Biology consisted of many clusters at each level of performance for students from each group. The content of the clusters obtained from both tests varied for performance level for students in all groups. In each case, the clusters were group-specific, and items within clusters were unstable. There was significant correlation between the two tests at high performance for urban girls, suburban boys and girls, but none for all other subgroups. The two tests were considered to measure different attributes. (Author/EB)