The objective of this study was to examine the effects of different culture systems on the development of early human embryos in vitro. A total of 460 fertilized oocytes from 82 cycles of patients was transferred into one of four systems: (1) into droplets of Ham's F10 medium + 12% normal human serum (NHS); (2) co-cultured on a human granulosa monolayer; (3) co-cultured with bovine oviductal epithelial cells (BOEC); or (4) co-cultured with bovine uterine epithelial cells (BUEC). The percentage of cleavage and the morphological appearance of embryos were recorded daily for 72 h in each system using an inverted phase-contrast microscope. The results showed that the proportions of the fertilized oocytes which developed to the four-cell stage 48 h after retrieval were, by culture system: (1) 70% (84/120); (2) 74% (85/115); (3) 78% (91/117); and (4) 76% (82/108). At 72 h after retrieval, the proportions of the eight-cell stage were, by culture system: (1) 45% (38/84); (2) 62% (53/85); (3) 75% (68/91); and (4) 70% (57/82). We concluded that a higher proportion of fertilized oocytes developed to embryos at the eight-cell stage in systems 2, 3 and 4 than in system 1. This indicates the beneficial effect of co-culture of human embryos with granulosa cell, BOEC and BUEC monolayers, which may be due to various factors.