['To test whether extension of the C-terminus of human chorionic gonadotropin (hCG) alpha-subunit (halpha) alters the bioactivity of the recombined alphabeta heterodimer.', 'The stop codon of halpha was mutated to produce a 24 amino acid extension.', 'The extended halpha (alpha(+24)) was co-expressed with hCGbeta in COS-7 cells and the receptor binding and in vivo bioactivity of the secreted hormone was compared with its wild-type counterpart.', 'This extension did not impair the binding of hCG to rat LH/CG receptors and provoked a sixfold reduction in its stimulatory activity of testosterone secretion in rat Leydig cells.'] Does human chorionic gonadotropin with C-elongated alpha-subunit retain full receptor binding and partial agonist activity?