The aim of this study was to partially characterize the glycoform composition of a recombinant human luteinizing hormone preparation (rhLH; Serono), an early version of the material (LHadi) which is currently being assessed for clinical application. Specifically, the charge (pl) and internal carbohydrate complexity of this rhLH was examined and compared with that of an alternative commercially available form of recombinant LH (Crystal Chem) and a pituitary International Reference Preparation (IRP). All preparations were separated by charge by chromatofocusing them on a pH gradient (7-4) using a 4 ml mono-P column is conjunction with a fast performance liquid chromatography system and by complexity of the oligosaccharide structures using concanavalin A (con-A) lectin affinity chromatography. LH in both the unfractionated and fractionated material was assessed by immunoradiometric assay (IRMA, I-LH) and by the in-vitro Leydig cell bioassay (B-LH). Both assays were calibrated against IRP 80/552. The in-vitro biopotency of the preparations was 18187 (Serono rhLH), 12063 (Crystal Chem rhLH) and 6658 (80/552) IU/mg; biological:immunological ratios were 1.14 (80/552), 1.90 (Crystal Chem rhLH) and 1.99 (Serono rhLH). However, similar qualitative data were obtained by both bioassay and immunoradiometric assay following fractionation, with the median pl of the bioactive LH in the preparations being 5.5 (24% > pH 6), 5.52 (18% > pH 6) and 4.97 (0% > pH 6) for the Serono, Crystal Chem and pituitary preparations respectively. Further all three contain < 1% of the complex carbohydrate structures and between 36-44% and 56-63% of the intermediate and simple forms of bioactive LH. In conclusion, the Serono recombinant LH preparation has a higher in-vitro bioactivity and is more basic than the other two preparations although the complexity of its carbohydrate moities appears to be similar.