Dissolution of progesterone, 19-nor-4-pregnene-3,20-dione and 6-methyl-17α-acetoxy-4,6-pregnadiene-3,20-dione was measured from lipid pellets of various composition. Values obtained in in vitro studies indicated that, after an initial period, the dissolution was constant. Studies in hamsters demonstrated that in vivo absorption declined with time at a rate similar to that observed with polydimethylsiloxane implants.