Received April 19, 2000
Accepted May 15, 2000

This paper reviews the use of co-culture in assisted reproduction. It has been suggested that co-culture procedures may have a significant beneficial impact on IVF, as it is believed that "factors" released by the co-culture cells. It has been argued that with conventional IVF the absence of various in vivo influences compromises the viability ofIVF embryos. We have therefore set out to look at the current status of co-culture by exploring the different methods and examining the rationale behind their use. We have not attempted a priori to answer the question of which is the best co-culture method nor is it clear in the current climate whether co-culture offers superior results to more modem sequential media formulations which have recently been reported to improve percentages of blastocysts for transfer as compared with traditional media. Our review of the literature leaves us with the following conclusion; the majority of published papers on co-culture, suggest that they have demonstrated significantly improved blastocyst rates (>50%), though no one has yet demonstrated unequivocally, how co-culture exerts this beneficial effect. demonstrated by the majority of co-culture studies, and the field is developing rapidly. Under the circumstances, although we feel that co-culture has much to offer as a research tool, for the time being, further research is required to characterise the factors that are involved, with a view to the future likelihood that these will be added to defined media, which now appear likely to supersede the need for coculture in the very near future.