The radioimmunoassay of alpha-subunit adapted in our laboratory was widely evaluated. Three different antisera (anti-pituitary alpha-subunit, anti-alpha-TSH and anti-alpha-hCG), the labelled preparations of pituitary alpha-subunit and alpha-hCG, and cross-reactivity with intact glycoprotein hormones (MRC standards of LH, FSH, hCG and TSH) were tested for their potential influence on the results of the assay. The basal levels of alpha-subunit were measured in 48 healthy young men, 48 normally menstruating women, 33 menopausal women, 37 pregnant women and 70 patients with pituitary adenoma. In addition a possibility of pulsatile secretion of alpha-subunit was investigated in 9 healthy young women, the ranges of alpha-subunit concentrations found were as follow (means +/- SD): 1.2 +/- 0.4 micrograms/l--in young men, 1.1 +/- 0.4 micrograms/l--in young women, 3.2 +/- 0.7 micrograms/l--in postmenopausal women, 1-54 micrograms/l--in pregnant women, and between 2.6 and 44.0 micrograms/l in 14 of 70 patients with pituitary adenoma. There were good correlations of results for 3 different antisera and their cross-reactivity with LH, FSH, hCG and TSH were just as low. In conclusion, the alpha-subunit assay appears clinically useful and should be widely applied in routine endocrinological diagnostics.