For many years, we have been using Ménézo B2 medium in our human in-vitro fertilization (IVF) programme. Ménézo B2 contains bovine serum albumin, which has in the meantime become less popular. The search for a valid alternative has therefore been initiated. In a first study from December 1993 to June 1994, we compared Ménézo B2 medium to Medi-Cult (Medi-Cult Universal IVF medium). In this auto-controlled study, sibling oocytes cultured in Ménézo B2 showed a normal fertilization rate similar to that for those cultured in Medi-Cult: 62.9 +/- 33.3 and 61.0 +/- 33.0% respectively (NS; paired t-test). In a second auto-controlled study conducted from November 1995 to March 1996, we compared Ménézo B2 to BM1 (Ellios Bio-Media) medium. The normal fertilization rate in the sibling oocytes was similar for those cultured in Ménézo B2 and in BM1: 66.9 +/- 27.5 versus 62.0 +/- 31.7% (NS; paired t-test). After further culture of the fertilized oocytes, no difference was apparent in either study as regards the morphological characteristics of the embryos cultured in the different media. The speed of development, however, did differ. In both studies, we observed a higher proportion of the embryos reaching at least the three- to four-cell stage at approximately 41 h post-insemination in Ménézo B2 medium than in either Medi-Cult or BM1. As regards the implantation potency of the embryos obtained in the different media, data were collected from the non-randomized transfers. These data indicate no difference between the media tested. This study indicates that the three commercial media with a different composition are equally able to sustain fertilization and embryo development until transfer.