Human postmenopausal serum and urine, and saline extracts of human pituitaries were gel-filtered on Sephadex G-100. The eluted fractions were radioimmunoassayed using 3 specificassays for native hLh, hLHα and hLHβ. The elution profile of immunoreactive components in postmenopausal urine exhibited 2 peaks of activity corresponding to those demonstrated for 125I-labeled hLH and hLHα. No LHβ was demonstrated. The immunoreactive components of postmenopausal serum eluted identically to 125I-LH, LHα and LHβ. In addition, a peak of immunoreactive LH material was observed in the pre-LH region of the elution profile, distinctly separate from the void volume. The percent of the total immunoassayable serum LH contained in this peak varied. In elution profiles of all pituitary extracts, LH, LHα and LHβ elution peaks corresponding to therespective labeled preparations were observed. An apparent excess of free a subunit was noted. All three antisera demonstrated immunoassayable LH material in the void volume. This large species contained a higher proportion of material reacting in the anti-hLHα system than did native hLH. Examination of the void volume material by electron microscopy indicated membrane material, but no ribosomes. Chemical assay failed to detect RNA. When void volume material was subjected to conditions which are known to (a) disrupt membrane continuity and (b) dissociate the noncova lently bonded subunits of native LH, this large species of LH failed to dissociate into smaller molecular species. These studies reveal: (1) an excess of free α subunit in the pituitary, serum and urine; (2) a large species of LH in the pituitary which upon analysis does not appear to be simple aggregation of LH, membrane entrapped native LH, or ribosomal bound LH.