During 48 days four young male, castrated Yorkshire x Landrace pigs (growers) were singly housed alternatively in standard pig pens (4 × 6 days) and metabolic cages (4 × 6 days). The faecal excretion of cortisol metabolites and immunoglobulin A (IgA) was quantified by enzyme-linked immunoabsorbent assays (ELISAs). The first stay in the metabolic cage was associated with an increase in faecal cortisol levels, which may be interpreted as a symptom of acute stress. But when the pigs' visits to the metabolic cages were repeated, the faccal cortisol generally reverted to fairly low levels. Concomitantly, faecal IgA excretion decreased steadily during the study period suggesting sustained stress. The body weight gain was lower during periods when the pigs were housed in metabolic cages than when they were in pens. These results suggest that metabolic cages caused a continued stress condition in pigs. One pig showed consistent high IgA excretion and a smaller decline in body weight gain during periods in the metabolic cage than the other pigs. This pig thus appeared to be less stressed than the other pigs, but maintained high cortisol levels throughout the study period when housed in the ordinary pen. This indicates that cortisol may have a protective effect against the stress caused by housing in metabolic cages.