PIP: The fluorescent staining method for determing the sex of the fetus is evaluated. Midcervical smears were obtained from 20 women who had elected a midtrimester abortion. The smears were stained with quinacrine hydrochloride and examined under a fluorescent microscope. 8 smears showed intranuclear fluorescent bodies that differed from typical Y chromatin. There was more than 1 spot in these smears, and they occurred with equal frequency in smears from mothers of both male and female aborted fetuses. Of the 8 smears with fluorescent spotting, 5 were male, and of the 12 smears without spots, 3 were male. Smears and sections prepared from the chorionic surface of 5 male and 5 female placentae showed inconsistent fluorescent spots, and the spots occurred with equal frequency in males and females. It was concluded that the multiple fluorescent spots in the nuclei make it almost impossible to distinguish Y chromatin and that the cells obtained from the midcervical smears do not afford a reliable predictor for prenatal sex determination.