The present invention is related to pyrrolidine derivatives of formula (I). Said ##STR00001## compounds are preferably for use as pharmaceutically active compounds. Specifically, pyrrolidine derivatives of formula (I) are useful in the treatment and/or prevention of premature labor, premature birth and dysmenorrhea. In particular, the present invention is related to pyrrolidine derivatives displaying a substantial modulatory, notably an antagonist activity of the oxytocin receptor. More preferably, said compounds are useful in the treatment and/or prevention of disease states mediated by oxytocin, including premature labor, premature birth and dysmenorrhea. The present invention is furthermore related to novel pyrrolidine derivatives as well as to methods of their preparation, wherein X is selected from the group consisting of CR6R7, NOR6, NNR6R7; A is selected from the group consisting of --(C.dbd.O)--, --(C.dbd.O)--O--, --C(.dbd.NH)--, --(C.dbd.O)--NH--, --(C.dbd.S)--NH, --SO22-, --SO2NH--, --CH2-, B is either a group --(C.dbd.O)--NR8R9 or represents a heterocyclic residue having the formula (a) wherein Q is NR10, O or S; n is an integer selected of 0, 1 or 2; Y, Z and E form together with the 2 carbons to which they are attached a 5 6 membered aryl or heteroaryl ring.