The authors conducted an open crossover trial of the biological activity of single-dose salmon calcitonin (sCT) 100 I.U. by nasal spray versus single-dose sCT 50 I.U. by intramuscular route in six healthy volunteers. The biological activity of the hormone was assessed on the changes in the blood levels of calcium, cAMP and osteocalcin recorded in the 4 h following administration. The increase in plasma cAMP shows that the hormone acts effectively by the nasal route. Further, the lack of statistically significant differences between the two modes of administration in any of the parameters considered demonstrates the bioequivalence of 50 I.U. of sCT i.m. and 100 I.U. of sCT intranasally.