Artifacts which simulate ova of Enterobius are frequently found in the “Cellophane” of the NIH swab, described by Hall (1937), used in diagnosis of pinworm infection. Attention is called to these artifacts in order to avoid possible confusion of them with pinworm ova. These artifacts are not superficial but are imbedded in the cellulose film and cannot be dislodged by surface scratching. They consist of a definite hyaline outline, usually ovoid, sometimes rounded, enveloping a dark, amorphous mass, the whole structure markedly similar to a pinworm egg. The hyaline outline, which appears to be composed of several layers, resembles the transparent shell layers of the egg of Enterobius. The central mass is irregular, brownish or greenish, with usually a clear space between it and the hyaline outline. Size variation is great but usually falls within the range of the pinworm egg, so that size and appearance constitute a potential source of error in diagnosis of oxyuriasis.