For the last three years a bronzing anomaly of cotton plants of the Mocó variety (Gossypium hirsutum L. var. maria galante Hutch.) has been recorded in the Seridó region (a semi-arid region in the north-eastern part of Brazil), state of Rio Grande do Norte. This anomaly was first thought to be of virus origin, but the observations reported in this paper indicated that it is due to the attack by a species of mite. Leaves from affected plants, especially those on the upper half of the branches, show a bronzing discoloration on the dorsal side, frequently accompanied by a rough and ventral side of these leaves shows some rugosity not present in normal leaves, and in most cases their edges curve downwards. In severe infestations the uppermost leaves on the plants may die and drop (plate 2, A and B). The mite responsible for bronzing of the Mocó cotton was identified by H. H. Keifer, Sacramento, Calif., as an undescribed Eriophyid species that also represents an undes-cribed genus. It has been referred to, tentatively, as Anthocoptes sp. until its description is published. Populations as high as 500 to 1,000 individuals per square centimeter of leaf area were encountered. This species of mite seems to be very sensitive to environmental conditions, as populations may drop within a short time from high numbers of mites per leaf to practically none.