The macroparasites Cephenemyia trompe (Modeer) and Hypoderma (=Oedemagena) tarandi (L.) (Diptera: Oestridae), Linguatula arctica Riley, Haugerud and Nilssen (Pentastomida: Linguatulidae), Elaphostrongylus rangiferi Mitskevich (Nematoda: Protostrongylidae), and abomasal nematodes (Nematoda: Trichostrongylidae) were sampled in semidomestic reindeer calves (Rangifer tarandus (L.)) (ca. 8 months of age) in northern Norway in 1988 (n=160) and 1989 (n=191). Each parasite showed an aggregated (clumped) distribution among the hosts and fitted the negative binomial distribution. Analyses of interspecific associations in intensities showed that there was no consistent covariation among the parasites apart from a weak correlation (Kendall's tau 0·104, P=0·007) between the 2 oestrids C. trompe and H. tarandi. This lack of covariation reveals that the parasites were distributed independently of each other, and suggests that innate host resistance is not a dominant factor that has a significant simultaneous effect on all parasites. The aggregated distribution of each parasite species is hypothesized to be caused by (1) random events and heterogeneities in host behaviour that create unequal transmission (exposure) rates, or (2) by heterogeneities in parasite specific immunocompetence among host individuals. Factors in hypothesis (1) are probably the most important at low transmission rates.