ABSTRACT. Endectocidal efficacy of doramectin administered intramuscularly at a dosage of 300 µg/kg was evaluated in 464 pigs naturally infected with intestinal nematodes or mange mites on 14 commercial farms in Japan. By doramectin treatment, fecal egg counts were reduced >99% for Ascaris suum, Strongyloides ransomi, Oesophagostomum dentatum, and For the trials against intestinal nematodes, fecal samples were collected from each animal immediately before treatment and on Days 7, 14 and 21 following treatment. Eggs in approximately 0.9 g fecal sample were enumerated using sugar centrifugal-flotation technique. According to the fecal egg counts derived before treatment, nine pigs with highest fecal egg counts were selected from each group for worm burden determination in Trial F. Then, surviving pigs among the pre-selected ones (9 from doramectin-treated and 8 from non-medicated control groups) were sacrificed on Day 21 following treatment.For the trials against sarcoptic mange, skin scrapings were collected from each animal immediately before treatment and on Days 7, 14, 21 and 28 following treatment. The skin scrapings were taken from an area of approximately 2 cm × 2 cm of mange lesion or the inner surface of an ear if no lesions were evident. The samples were digested in 10% NaOH overnight, then mites including adults, nymphs and larvae, and mite eggs were counted under the microscope. On the same days when scrapings were collected, the severity of skin lesion and pruritus were scored from 0 to 3, and from 0 to 2, respectively, using the score index as follows -(1) for skin lesion: 0=no active lesions, 1=no hyperkeratotic mange lesion, but slight lesions of encrustation, scaling or erythema, 2=a few localized moderately thick dry grayish-white crusty lesions, 3=large, thick, grayish, rough and dry crusts with coalescence of lesions, (2) for pruritus: 0=no scratching and rubbing, 1=low frequency of scratching and rubbing, 2=high frequency of scratching and rubbing.During the study period, control and treated groups were accommodated in separate pens on concrete floors in all trials except Trial H in which control and treated groups shared a single room with fermented sawdust litter.Fecal egg counts of A. suum, O. dentatum, T. suis, and of S. ransomi in the doramectin-treated groups decreased