TSH from human serum was separated into classes by serial lectin affinity chromatography using Concanavalin-A (ConA), lentil, and ricin lectins. TSH from 10 euthyroid subjects, 40 patients with primary hypothyroidism, and 1 patient with central hypothyroidism was studied. The patterns of ConA and lentil affinity binding were similar for diverse patients; forms of TSH that bound firmly to ConA also tended to bind firmly to lentil. Differences in TSH-ricin binding suggested that there were differences in the sialylation of TSH in sera of euthyroid, primary, and central hypothyroidism patients. For euthyroid subjects, 16.1 +/- 5.4% (mean +/- SD) of the TSH bound to ricin, while after neuraminidase treatment, 38.4 +/- 5.4% bound. For patients with primary hypothyroidism, 23.5 +/- 6.0% of the TSH bound to the ricin, while after neuraminidase treatment, 65.7 +/- 8.8% bound. The increase in ricin binding induced by neuraminidase treatment was significantly higher for TSH from patients with primary hypothyroidism than in that from euthyroid subjects (42.3 +/- 7.6% vs. 22.3 +/- 4.4%; P less than 0.01) and was greater for long term than for short term hypothyroid patients (49.5 +/- 5.0% vs. 36.5 +/- 6.5%; P less than 0.01). While 30% of native TSH from the serum of the patient with central hypothyroidism bound to ricin, the amount bound increased only 17.6% after neuraminidase treatment. McKenzie bioassay of pituitary-derived TSH that was similarly fractionated using ricin failed to show detectable differences in bioactivity among the lectin column fractions. Thus, 1) circulating human TSH can be consistently separated into discrete classes using serial lectin affinity chromatography; 2) there is relatively more core fucosylation of the less processed high mannose and hybrid forms of TSH and less core fucosylation of more processed complex forms; 3) ConA and lentil binding of TSH in primary and central hypothyroidism is similar to that in the euthyroid state; 4) patients with primary hypothyroidism have more sialylated TSH than a patient with central hypothyroidism or euthyroid subjects; and 5) the degree of TSH sialylation increases with prolonged primary hypothyroidism.