A study on the development and effect of experimental Sarcoptes scabiei var suis infestations in growing pigs is described. Pigs were infested at either weekly or fortnightly intervals throughout each experimental and individual growth rates and feed conversion ratios were determined. The animals were fed diets which contained either optimal or sub-optimal levels of protein. They were housed either intensively or extensively. In all experiments the majority of infested animals developed a generalised hypersensitivity to sarcoptes mites and performed significantly less efficiently than non-infested littermates. Mean growth rates were depressed from 9.2 to 12.5 per cent and feed conversion efficiencies by a similar margin. Well fed, intensively housed pigs developed a more severe hypersensitivity reaction than poorly fed, extensively housed pigs.