A prospective randomized placebo controlled clinical trial was carried out on 250 patients (cycles) considered at risk of developing OHSS in an IVF programme. Criteria for inclusion were: estradiol value of more than 3000 pg/ml or the presence of more than 20 follicles on the day of hCG administration. Patients were randomized by using a random table to receive either 20% human albumin 50 ml (n: 82); 6% hydroxyethyl starch (200/0.5) 500 ml (n: 85) or a placebo of 500 ml 0.9% NaCl solution (n: 83) over 30 min during oocyte collection. Groups were similar with respect to patients' age, estradiol levels on hCG day, body mass index, number of oocytes retrieved, number of embryos transferred and pregnancies (P>0.05). There was no severe OHSS in patients who received albumin and HES while four patients who received placebo developed severe OHSS. On the other hand moderate OHSS was encountered in four patients in the albumin group; five patients receiving HES; and 12 patients receiving placebo. There was a statistically significant difference in the incidence of moderate, severe and overall OHSS among groups (P values of <0.05, <0.05, and <0.01, respectively). Both HES and albumin significantly reduced the incidence of moderate, severe and overall incidence of OHSS. It is concluded that hydroxyethyl starch is a cheaper and safer alternative to Human Albumin in OHSS prevention.