Mixtures of 3E and 3Z isomers of 3-(O-(2-carboxyethyl)oxime (CEO) derivatives of testosterone and 17 alpha-methyltestosterone were prepared by reaction with (O-(2-carboxyethyl))hydroxylamine. These isomers were separated after conversion into methyl esters, and mild alkaline hydrolysis recovered pure E/Z-isomers of 3-CEO derivatives of testosterone and 17 alpha-methyltestosterone. By the same method, after oximation, methylation, and separation, (20R)-20-hydroxypregn-4-en-3-one gave (3E,2OR)-20-hydroxypregn-4-en-3-one 3(O-(2-carboxyethyl)oxime and (3Z,20R)-20-hydroxypregn-4-en-3-one 3-(O-(2-carboxyethyl))oxime methyl esters. The oxidation and subsequent hydrolysis of these compounds produced 3E and 3Z isomers of the 3-CEO derivative of progesterone. Pure E/Z-isomers of 3-CEO derivatives are designed for the development of immunoanalytical systems, which make use of the bridge heterology based on the geometric isomerism.