Transmission electron micrographs of the cuticle of adult Heligmosomoides bakeri exposed to crude papaya latex (CPL) (200 μM). After 10 minutes exposure the cuticle starts to exhibit swelling and wrinkling of the surface with the appearance of electron dense material and collapse of the cretes. Following 30 minutes of exposure to papaya latex much of the structure of the cuticle has been lost and detachment of the cuticle from the underlying hypodermis is apparent in places. For TEM preparation adult specimens of Heligmosomoides bakeri were fixed in glutaraladehyde, postfixed in osmium tetroxide, dehydrated in ethanol embedded in epoxy resin and sectioned. The sections were stained in lead citrate and uranyl acetate and examined in a Jeol 1010 transmission electron microscope.