‘Zona drilling’ was the term used originally to denote the technique of creating a hole in the ZP surrounding the oocyte (Gordon and Talansky, 1986). The first intuitive application of this procedure in human infertility was to provide a conduit via which spermatozoa could pass through the ZP (Cohen et al., 1988; Gordon et al., 1988). This approach to alleviating male-factor forms of infertility that were related to the inability of spermatozoa to bind to or penetrate the ZP was termed partial zona dissection (PZD). This involved physically cutting a hole or slit in the ZP using micropipettes. However, this approach was considered to be inefficient because it was suspected that partial or complete closure of the slit created might compromise sperm motility or even prevent access to the oocyte altogether. Therefore, the next logical step was to use ZD as a means of introducing spermatozoa directly into the PVS with the aid of a large microinjection pipette that could be passed through the hole thus created (Laws-King et al., 1987; Ng et al., 1988). This technique, originally termed ‘microinjection sperm transfer’ later became known as ‘subzonal insemination’. With the introduction of very fine and sharp microinjection pipettes, ZD soon became unnecessary for the SUZI technique, as it became possible to pierce the ZP directly. Osmotic manipulation of the oocyte prior to SUZI was usually applied to enlarge the PVS, so as to avoid damage to the oolemma.