In the analysis of steroid hormones careful attention is usually paid to blood collection and plasma storage. However, the appropriate care of samples cannot always be assured in routine work with steroids. Therefore, the stability of cortisol, aldosterone, 17-hydroxyprogesterone, testosterone, androstenedione, dehydroepiandrosteronesulphate, oestrone, oestradiol, sex hormone binding globulin (SHBG) and, the binding of testosterone and cortisol to plasma proteins in blood and plasma were studied before and after various handling procedures. Ten cycles of alternate freezing and thawing of plasma did not significantly affect the levels of the steroids or their plasma binding. The greatest differences, compared with controls, were seen for aldosterone (-6.2%) and oestradiol (-5.3%). Plasma storage at -28 degrees C was hardly superior to a 4 days storage at 4 degrees C (refrigerator) or 22 degrees C (room temperature). Although androstenedione (-10.9%), oestrone (-10.2%) and oestradiol (-12.2%) levels decreased by more than 10%, the means of all analyses were still in the 2 SD range. Even SHBG and the steroid binding were only slightly affected by temperature. When whole blood was stored at 4 degrees C or 22 degrees C, the resulting values differed from those obtained with plasma, but the differences were usually less than 10%. Although the levels were within the 2 SD range, whole blood showed a decrease of 12.3% for aldosterone and 14.5% for androstenedione. In contrast, plasma binding of testosterone (25.9%) and cortisol (15.1%) were substantially affected by storage at 22 degrees C in whole blood. It is concluded that repeated freezing and thawing of plasma, or storage at various temperatures have only a small effect on the measured levels of steroids and their plasma binding. Although it is not advisable, even whole blood may be used for the analysis of steroid concentrations.