The present experiments compared the maturational and developmental competence of immature oocytes derived from stimulated cycles, following culture in a newly designed in-vitro maturation medium (IVM-medium) or in standard tissue culture medium (TCM-199; control). The results indicated that maturation and fertilization rates were comparable when the cumulus-free M-I stage oocytes were matured in the IVM-medium (78.6%) or the control medium (70.8%). However, there was a significant difference in blastocyst development (P < 0.05) when M-I oocytes were matured in these two media (19.6 versus 7.7%). Both maturation and early embryonic development rates of GV-stage oocytes were significantly higher (P < 0.01) in the IVM-medium (maturation: 75.7%; blastocyst: 12.9%) compared with control (maturation 55.7%; blastocyst: 0.0%). Moreover, embryos developed to the blastocyst stage at a higher rate in both media if GV-stage oocytes had matured within 24 h compared with 48 h of culture. These results demonstrate that immature human oocytes derived from stimulated ovaries can achieve maturation and early embryonic development in vitro, especially in the new IVM-medium, which may allow additional embryos to be produced for clinical use at embryo transfer.