Increased knowledge concerning the levels of estrogen in normal and abnormal reproductive physiology has been made possible because of significant development in the chemical determination. But present day chemical estrogen measurements are still based upon the general principles described by Brown of hydrolysis, extraction, purification, fractionation, and .finally, quantitative estimation. After the use of numerous modifications of colorimetry, ,fluorometric quantitative estimation has been developed and increased in sensitivity. Still -further specificity and sensitivity was obtained by the use of thin layer chromatography, gas -chromatography, and radioisotopic tracers. The gradual combination of these methods has brought the sensitivity of some.of the techniques to two nanograms of estrogen, sufficient for the estimation of estrogens in the plasma ,of nonpregnant women.
The use of gas chromatography appears to be most promising from the point of view of sensitivity and rapidity, but -for the assessment of estrogen levels in nonpregnant females, gas ,chromatography must be preceded by thin layer.
On the other hand, bioassay methods, such as the use of rat uterine weight method or :intravaginal assay ;method,- have served _reasonably well and continues to do so at the present -time .for most clinical problems.
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