The occurrence and host-parasite relationships of three acanthocephalan species parasitizing white suckers, Catostomus commersoni (Lacepede), from two rivers in southeastern New Hampshire were studied. The mean intensity of Neoechinorhynchus cristatus Lynch 1936 was highest in Oyster River white suckers during fall 1975 and 1976. Conversely, the mean intensity of Pomphorhynchus bul- bocolli Linkins in Van Cleave 1919 was highest in spring and summer 1975, spring 1976, and winter 1976-1977. This seasonal pattern coincided with the movement of large suckers into and out of the Oyster River sampling area, and the subsequent examination of large and small hosts. Octospinifer macilentus Van Cleave 1919 and P. bulbocolli infected a large number of Bellamy River white suckers, and did not exhibit seasonal infection patterns. All three acanthocephalan species occurred in the mid- to posterior intestinal area. Significant correlation coefficients suggested that prevalence and/or mean intensity of 0. macilentus and P. bulbocolli (both localities) increased as did fish length. The prevalence and mean intensity of N. cristatus were highest in fish between 5.0 and 14.9 cm in length. Male and female white suckers had similar prevalences and mean intensities. spectively. Fish were taken to the laboratory alive, measured, sexed, and necropsied within 36 hr of capture. The entire alimentary canal (from the esophagus to the vent) was removed. It was divided into five segments based on percentages of the total length from the anterior end (0-20%, 20-40%, 40- 60%, 60-80%, and 80-100%). These segments are designated 1, 2, 3, 4, and 5, respectively. The po- sition, number, degree of development, and sex of the acanthocephalans recovered from each segment were recorded. The rivers and sampling procedure were described in Muzzall (1980). Acanthocepha- lans were fixed and stained using standard tech- niques. Female Neoechinorhynchus cristatus and Octo- spinifer macilentus were divided into three devel- opmental stages: 1) immature-ovary not fragment- ed; 2) ovarian balls present; and 3) gravid-ovarian balls and eggs present, as well as those with eggs only. Indistinct sperm ducts, approximately 2 mm in length or less, in stained males of both species indicated immaturity. Larger males were consid- ered to be adults. Immature female and male N. cristatus and 0. macilentus were considered to be members of the recruitment portion of the parasite