Abstract: "Partial" and "complete" CTP units are used to modify biologically active proteins and peptides to alter their clearance patterns. "Complete" CTP units have the amino acid sequence found at positions 112-118 to position 145 of the .beta.-subunit of human chorionic gonadotropin; "partial" CTP units are missing at least one amino acid in the region of position 118-145 inclusive. Variants of these CTP units contain 1-5 conservative amino acid substitutions which do not destroy activity. Suitable peptides or proteins which may be modified in this manner include various hormones and cytokines.