The effects of systemically administered calcitonin (CT) on granulation tissue development were compared using viscose cellulose sponges as wound model in the rat. The ingrowth of new granulation tissue was analyzed for the contents of various connective tissue components (total nitrogen, hydroxyproline, DNA, and RNA) and for the differential counts of the cells infiltrating the sponges. The results indicate that up to 4 weeks postoperatively (p.o.) CT did not affect the net amount of collagen, measured as hydroxyproline, total nitrogen, aminosugars nor the dynamics of differentiation and viability of the invading cells. The present observation that CT has negligible effects, if any, on the early stages of connective tissue formation and on the cell population indicates that surgical procedures could be carried out safely during systemic CT therapy without an increased risk of wound complications.