Larval haemocytes of Anticarsia gemmatalis (Lepidoptera: Noctuidae) are presented and classified based on morphological characteristics. Haemolymph samples collected from 3rd to 6th instar larvae were observed using differential interference contrast microscopy as well as processed for transmission and scanning electron microscopy. Five general types of haemocytes were observed: prohaemocytes (Pr), plasmatocytes (Pl), granular haemocytes (GH), oenocytoids (Oe) and spherulocytes (SPh). Granular haemocytes were subdivided into two morphologically different subtypes (GH 1 and GH 2). Phenoloxidase activity was clearly observed in the Oe, and also less intensely in the Sph. The osmium/imidazole buffer technique revealed that GH 2 accumulated numerous, small lipid vesicles among their granules, while Pl contained larger but less numerous lipid inclusions. Total haemocyte counts varied between 12.3 and 20.9 x 10(3) haemocytes/microl. Pl, GH 1 and Sph were the cell types more frequently observed in all larval stages studied. GH 2 were rare in 3rd and 4th instars, becoming more numerous after the inception of the 5th instar. Populations of GH 1 and Sph maintained their proportions throughout larval development. Populations of Oe, Pl and Pr, however, presented more marked variations in their proportions. Ultrastructural studies were shown to be useful for the identification and classification of haemocytes, facilitating further analysis by light microscopy.