['To evaluate the usefulness of microfilament disruption before enucleation and nuclear transfer in human oocytes at different stages of maturation.', 'Prospective experimental study.', 'Private clinics.', 'Infertile couples undergoing assisted reproduction attempts.', 'Oocyte enucleation and nuclear transfer, activation of reconstructed oocytes.', 'Oocyte survival, nuclear transfer efficacy, activation outcomes.', 'Survival rate and nuclear transfer efficacy of germinal vesicle oocytes exposed to the microfilament disrupting agent cytochalasin B before enucleation were 88% and 80%, respectively. These figures dropped, respectively, to 8% and 2% when cytochalasin treatment was omitted. By contrast, cytochalasin-treated and -untreated metaphase II oocytes showed similar survival rate (87% vs. 90%) and nuclear transfer efficacy (78% vs. 87%). This also applied to metaphase II oocytes matured in vitro from the germinal vesicle stage. Cytochalasin treatment did not affect activation rate of reconstructed oocytes, but it increased the occurrence of oocytes with multiple female pronuclei.'] Is microfilament disruption required for enucleation and nuclear transfer in germinal vesicle but not metaphase II human oocytes?