The effects of porcine relaxin (Rlx; 3,000 U/mg) combined with cloprostenol (Clo) or dexamethasone (Dex) on pelvic and cervical dilatation and dystocia were investigated in crossbred beef heifers ( n = 60). Clo (500 μg, im, n = 30) or Dex (20 mg, im, n = 30) was given at Day 273, 10 days before expected parturition (Day 283). Heifers were assigned at random within Clo ( n = 20) and Dex ( n = 20) groups to receive Rlx (1 mg, n = 5/treatment) im (IM) or into the cervical os (OS) at 0 h (the time of Clo or Dex treatment) or 24 h later. In lieu of Rlx, IM controls received 0.01 M phosphate buffered saline (PBS, 1 ml, im, n = 5) and OS controls received 0.01 M Gel-PBS (1 ml, os, n = 5). Pelvic area increased ( P < 0.01) 10.7 ± 1.67, 3.6 ± 1.25, 12.6 ± 2.60 and 5.4 ± 1.01 cm 2 (mean ± SE) from pretreatment mean deviations at 24 h for Rlx + Clo, Clo, Rlx + Dex, and Dex, respectively. Similarly, cervical dilatation increased ( P < 0.001) 2.4, 0.6, 2.5 and 0.8 cm for Rlx + Clo, Clo, Rlx + Dex, and Dex, respectively. Route of administration (im or os) and time (0 or 24 h) of relaxin treatment affected ( P < 0.05) pelvic area and cervical dilatation within 24 h. The incidence and severity of dystocia were reduced by relaxin ( P < 0.05), 70 and 45% calving ease and 2.0 and 2.5 dystocia score for relaxin and control heifers, respectively. Thus, induction of parturition with relaxin combined with cloprostenol or dexamethasone reduced the incidence of dystocia as a result of increased pelvic and cervical dilatation in first-calf beef heifers.