Each panel shows the results of analysing pairs of samples from 10 postmenopausal breast cancer patients. Light column, measured serum oestradiol before treatment (Pre); dark column, result during the use of the aromatase inhibitor, anastrozole. (a), (b) Results obtained when the oestradiol was measured by direct assay: (a) Beckman Coulter Access Immumoassay system Estradiol 33540, and (b) DSL 3rd Generation Estradiol Radioimmunoassay DSL-39100. (c), (d) Results when the oestradiol is measured after a pre-extraction with an organic solvent: (c) extraction and radioimmunoassay (as used at the Royal Marsden ), and (d) the DSL-39100 kit after pre-extraction of serum samples with diethyl ether. Arrows indicate the detection limits for the assays; no arrow in (d) since this analysis was performed for the present study only and no detection limit was determined.