angiostrongylus vasorum, the french heartworm, and crenosoma vulpis, a lungworm, infect the pulmonary arteries and the bronchi and bronchioles, respectively, o f red foxes (vulpes vulpes). both are widespread in europe, but within north america the distribution of a. vasorum is limited to the island of newfoundland, canada. during 2000-2002, 366 fox carcasses were collected from 6 regions o f the island. this study is unique in being the first large-scale survey of a. vasorum and c. vulpis in a natural fox population. its objectives were to determine the precise distribution o f both parasites in newfoundland and to examine the possibility of interaction between them. crenosoma vulpis occurred in all 6 regions at an overall prevalence o f 87% and a mean intensity o f 230 ± 20.8 (mean ± s.e.). young-of-the-year foxes had higher mean intensities (260 ± 39.4) than yearlings (91 ± 31.2) or adults (78 ± 41.1) (f[2, 153] = 11.07, p < 0.001). the intensity o f c. vulpis was not related to host sex, omental fat ratio, or body fat index. there was a weak positive relationship between number of adult worms and output of first-stage larvae in feces (r2 = 0.199, ff[1,135] = 34.84, p < 0.001); larval output decreased with increasing fox age (f[2,127 ] = 18.99,p< 0.001). angiostrongylus vasorum occurred only in the 3 southeast regions of the island; the avalon peninsula, the north east coast, and the south coast/burin peninsula. its distribution may be limited by cold temperatures as it did not occur in areas where mean winter temperatures were lower than -4°c . the prevalence was 56% and mean intensity 72 ± 7.6. the number of adult worms did not differ with host age, sex, omental fat ratio, or body fat index. although named the french heartworm, 88% of all a. vasorum were recovered from the pulmonary arteries while the remainder were in the right ventricle. however, 78% o f infected foxes had at least one worm in the right ventricle. although the number of a. vasorum did not differ between the pulmonary arteries o f the left and right lobes (f[1, 164] = 1.70, p= 0.194), there were more worms in the arteries o f the posterior lobes (47 ± 5.4) than in the anterior (24 ± 2.5) (f[1, 161] = 13.39, p < 0.001). also, there were no relationships between the number of a vasorum and larval output, heart weight ratio, or ventricular ratio. although 40% of foxes from the a. vasorum positive regions had both a. vasorum and c. vulpis infections, there was no interaction between the two parasites (gc[1] = 0.10). furthermore, there was no linear relationship between the two parasites, and the mean intensity of each nematode did not differ between single and dual infections. eight coyotes (canis latrans) from newfoundland were also examined. none had a. vasorum, but 38% had c. vulpis, although the mean intensity (16 ± 10.2) was lower than that in foxes.