To investigate 405 cases of persistent low concentrations of human chorionic gonadotropin (hCG).The USA hCG Reference Service measured total regular hCG, follicle stimulating hormone and luteinizing hormone (LH) with the Siemens (New York, New York) Immulite 1000 assay. Hyperglycosylated hCG, nicked hCG, C-terminal peptide total hCG, intact regular hCG, free beta-subunit and beta-core fragment were measured in manual microtiter plate assays.Four cases of inherited hCG were identified, with similar hCG production recorded in first degree relatives. All cases produced primarily the regular hCG dimer. In 1 case hCG was detected only in the urine sample.Inherited hCG is disclosed as a source of persistent low concentrations ofhCG. It was assumed that this regular hCG is produced by the pituitary gland, either as excess pituitary production beyond that which occurs alongside the LH peak in every menstrual cycle or as a genetic disorder.