The relative proportion of the circulating luteinizing hormone isoforms in goats during follicular phase (pre-ovulatory peak; F) and anestrus (A) was investigated. Estrus was synchronized in six goats with a prostaglandin analogue. After estrus was detected, blood samples were taken at 1 h intervals for 24 h. Four anestrous goats received 100 microg i.v. of GnRH and blood samples were collected every 15 min for 5 h. Samples with the greatest LH concentration in follicular phase and after GnRH administration (anestrus) were analyzed by chromatofocusing and eluted with a pH gradient from 10.5 to 3.5. For quantification purposes eluted LH was grouped into basic (pH> or =7.5), neutral (pH 7.4-6.5) and acidic isoforms (pH< or =6.4) as well as by pH unit. In both physiological conditions (PC), basic and acidic isoforms were greater than the neutral. With this grouping criteria, there was an interaction between PC and pH group, with the proportion of neutral isoforms being greater (p or =10), which amounted to a percentage of 6.0+/-0.4% of the total observed during A, and 3+/-1% during F (p