The development of adult worm burdens and microfilaremias were determined in jirds which received 2, 3, or 4 subcutaneous inoculations of 50 Brugia pahangi infective larvae. Parasite burdens in multiply inoculated jirds were compared to those in four different groups of jirds which received single inoculations of 50 infective larvae. One of each of these singly inoculated groups was infected on the same day that one of the inoculations was given to the multiply infected jirds. Thus, the duration of the infections in the four groups of jirds receiving one inoculation was 54, 118, 189, and 254 days. The development of lymphatic lesions and granulomatous hypersensitivity to B. pahangi antigen was assessed in all jirds at necropsy. The percentage recoveries of adult worms and their locations did not differ in the singly inoculated jirds with infections of different durations. A protective resistance to reinfection, as measured by adult worm recovery in multiply infected jirds, did not occur. The lymphatic lesion scores and numbers of intralymphatic thrombi was greatest in singly inoculated jirds examined 54 days after infection. Pulmonary granuloma areas around adult filarial antigen coated beads embolized in the lungs of jirds 3 days prior to necropsy were also greatest in singly inoculated jirds examined 54 days after infection. Using criteria of lesion scores and lymph thrombi numbers to assess lymphatic lesion severity, a decrease in lesion severity as well as pulmonary granuloma size around antigen coupled beads was seen by 118 days after infection in singly inoculated jirds. Lymphatic lesion scores, lymph thrombi numbers, and areas of pulmonary granulomas around antigen coupled beads in jirds which received 2 or 3 inoculations of 50L 3 were similar to those in singly inoculated jirds examined at times greater than 54 days after infection. Lymphatic lesion scores and numbers of lymph thrombi in jirds receiving four inoculations were similar to those in singly inoculated jirds examined at 54 days after infection. However, the lymph thrombi observed in this multiply infected group were generally larger than those seen in singly inoculated animals. The increased number of lymph thrombi observed in jirds receiving four inoculations was not accompanied by a corresponding increase in pulmonary granuloma areas around antigen coupled beads. Pulmonary granulomas around diethanolamine coupled beads, used as a measure of foreign body inflammatory reactivity, did not differ between groups. Antibody titers to crude soluble adult worm antigen measured by enzyme-linked immunosorbant assay, reached their maximal titers within 50 days after infection in all jirds. The titers did not change markedly with the duration of infection or with additional inoculations of infective larvae.