The present invention is directed to the neutralizing prolactin receptor antibody Mat3, and antigen binding fragments, pharmaceutical compositions containing them and their use in the treatment or prevention of benign disorders and indications mediated by the prolactin receptor such as endometriosis, adenomyosis, non-hormonal female contraception, benign breast disease and mastalgia, lactation inhibition, benign prostate hyperplasia, fibroids, hyper- and normoprolactinemic hair loss, and cotreatment in combined hormone therapy to inhibit mammary epithelial cell proliferation and for the treatment and prevention of antiestrogen-resistant breast cancer. The antibody of the invention blocks prolactin receptor-mediated signalling.