New formulations are described containing a calcitonin as active principle and suitable for rectal administration in the form of soft gelatin capsules, in which the active principle, possibly mixed with a stabilizer, is dispersed in a liquid vehicle consisting of a polyethyleneglycol or a mixture of polyethyleneglycols of different molecular weight which has the consistency of a homogeneous fluid at ambient temperature, and possibly a C₂-C₆ alcohol with at least 2 hydroxyl groups, and present in a weight quantity of less than 15%. Said formulations, which contain no absorption adjuvant, enable the same pattern of hematic levels to be obtained as obtainable by conventional intramuscular administration, for equal unit dosages. Moreover, the absence of water makes said formulations highly stable.