Eggs of Tyrophagus putrescentiae (Schrank) were examined with both scanning (SEM) and transmission (TEM) electron microscopes. The eggs, cylindrical in shape, exhibit an external surface studded with raised irregular mounds and with Iocular chambers. Other significant details, as revealed at the SEM leve!, are the absence of aeropyles and the Jack of a specialized micropyIar area. TEM demonstrates that the egg sheii consists of two layers: an inner translucent layer and outer layer of mounds and Iocular chambers open at their bases. The present results and the question of egg sheii origin in Acarina are discussed and compared with those of the other arthropodan eggs.