Oxidative stress is important for promoting oocyte maturation and ovulation within the follicle through calcium ion (Ca2+) influx. The relationship between antioxidant and cytosolic Ca2+ levels and oocyte quality and fertilisation rate in the granulosa cells of patients undergoing in vitro fertilisation was investigated. Granulosa cells were collected from 33 patients. Cytosolic free Ca2+ ([Ca2+](i)) concentration, lipid peroxidation, reduced glutathione, glutathione peroxidase and oocyte quality were measured in the granulosa cells. The relationship between two drug protocols was also examined (gonadotrophin-releasing hormone antagonist and agonist protocols) and the same parameters investigated. The [Ca2+](i) concentration (P < 0.001), glutathione (P < 0.05) and oocyte quality (P < 0.001) values were significantly higher in the fertilised group than in the non-fertilised group, although glutathione peroxidase activity was significantly (P < 0.05) higher in the non-fertilised group than in the fertilised group. The [Ca2+](i) concentrations were also higher (P < 0.001) in the good-quality oocyte groups than in the poor-quality oocyte group. There was no correlation between the two drug protocols and investigated parameters. In conclusion, it was observed that high glutathione and cytosolic Ca2+ concentrations in granulosa cells of patients undergoing in vitro fertilisation tended to increase the fertilisation potential of oocytes.