Although different FSH preparations and injection regimens are used to superovulate cattle, the optimum treatment regimen and blood concentrations of FSH to induce effective superovulatory responses are currently not known. The current objective was to evaluate the pattern of follicular growth, oestradiol-17 beta(E2) concentrations and yield of embryos in heifers following superovulation with two different pFSH preparations reportedly differing in LH content. In experiment 1, 90 synchronised heifers were superovulated at mid-cycle using a 2 x 2 factorial design comparing Folltropin (Vetrepharm; low LH) with Pluset (Serovet; FSH:LH ratio 1:1) administered either as a single or multiple (8 for Folltropin, MF and 10 for Pluset, MP) injections. Animals were inseminated during oestrus which was induced with prostaglandin F2 alpha analogue and embryos were recovered 7 days later. Overall, Pluset treatments compared with Folltropin resulted in more ovulations and unfertilized or degenerate embryos (P < 0.05). Multiple injections resulted in more (P < 0.05) freezable (MF = 55 +/- 1.2; MP = 3.8 +/- 1.0) and transferable embryos (MF = 2.68 +/- 0.9; MP = 2.71 +/- 0.9) than single injections (SF = 2.2 +/- 0.5 and 1.0 +/- 0.3 respectively; SP = 2.6 +/- 0.8 and 1.3 +/- 0.4 respectively); there was also a higher (P < 0.05) percentage embryo recovery rate. In two subsequent experiments, animals (n = 17) were superovulated with either single or multiple injections of Folltropin or Pluset as described and blood samples were collected and analysed for E2 concentrations. Ovarian scanning was carried out until 72 h after the first FSH injection, to count medium (5-9 mm) and large (> or = 10 mm) follicles. Heifers treated with SP had higher E2 concentrations in comparison with heifers treated with SF at 18, 36-48 and 84-96 h after the FSH injection. There were no differences in E2 concentrations in heifers treated with MF or MP treatments. Heifers treated with SP had greater numbers of follicles compared to SF treated heifers (21.0 +/- 3.1 vs 13.9 +/- 2.2; P = 0.089) on the third day after FSH injection. There were no differences between the numbers of medium and large follicles in heifers treated with MF or MP at any time throughout the experimental period. These data indicate that a single injection of Folltropin or Pluset can result in multiple ovulations and that the E2 profiles are different following single injections of either Folltropin or Pluset.