The effect of temperature fluctuation on spindle integrity and chromosomal organisation in the human oocyte, and the consequences of such effects on the chromosomal constitution of resulting parthenotes, were investigated. A total of 340 oocytes were stained immunocytochemically with an antibody to α-tubulin, and 502 were activated parthenogenetically. Exposure of oocytes to room temperature for 2, 10 or 30 min caused disruption of the spindle in 77%(n = 26),72%(n = 18) and 89% (n = 19) of cases respectively, with evidence of chromosomal dispersal in 50%,56% and 52.6% respectively. These effects were reversed when oocytes were returned to 37°C after exposure to room temperature for 2 min, but not after 10 min or 30 min: Temperature reduction affected rates of parthenogenetic activation of oocytes (2 min: 67%, n = 27; 10 min: 68%, n = 28; 30 min; 54%, n = 35) and cleavege of resulting parthenotes, but only if oocytes were exposed to room temperature for 30 min (30 min: 53%, n = 19).There is a direct association between temperature-induced spindle damage in the oocyte(70%, 50 of 63) and chromosomal abnormalities in parthenotes developed from oocytes exposed to room temperature (56%,23 of 41; P < 0.01).