White-tailed deer (Odocoileus virginianus) obtained from Noxubee National Wildlife Refuge, Noxubee County, Mississippi (USA) during April (n = 3), June (n = 5), September (n = 5), and November (n = 5) 1989, were necropsied for counting and identification of adult and larval stages of abomasal nematodes. Fourth-stage larvae (L4) (n < or = 25) from each deer were randomly selected for measurement of total worm length and width. Adults of four worm species were found: Mazamastrongylus odocoilei, M. pursglovei, Ostertagia mossi, and O. dikmansi. There were no differences between months in adult male worm burdens for all species except O. dikmansi for which the April worm burden was greatest (P < or = 0.05). Overall, the length of L4 ranged from 929 to 4,361 microns. There were no significant differences (P > 0.05) between months in the mean length (1,334 to 1,532 microns) of L4. Except for low numbers of developing fourth-stage larvae (length > 1,650 microns) in April (2.6%), June (7.4%), September (11.3%), and November (3.7%), worms were early fourth-stage larvae (EL4) or fully developed adults. Overall, the proportion of EL4 in individual deer ranged from 19 to 97%; in male (n = 3) and female (n = 15) deer the proportions of EL4 were 22.5% and 67%, respectively. The mean proportions of EL4 in female deer were 51.4% (April), 63.2% (June), 78.1% (September), and 74.7% (November), but there was no difference (P > 0.05) among the 4 months.(ABSTRACT TRUNCATED AT 250 WORDS)