Some (bromo- and/or (iodo-methyl)dimethylsilyl ethers of testosterone, androsterone, dehydroepiandrosterone, estradiol monomethyl ether, and Δ1-testosterone have been prepared and shown to be suitable for use in gas chromatographic analyses. The relative responses of a 63Ni electron-capture detector to corresponding iodo-, bromo-, and chloro-compounds are in the approximate ratios of 50 : 18 : 1. Good chromatograms, suitable for quantitative analysis, can be obtained with 1 ng. of the ethers, and with as little as 0·1 ng. for the iodo-compounds. The (iodomethyl)dimethylsilyl ethers can be prepared very simple by treating the corresponding chloro- or bromo-compounds with sodium iodide in acetone.