Daily oral administration of o,p'-DDD to dogs produced glucocorticoid deficiency. This was demonstrated by a decreased plasma hydroxy corticosteroids (17 OHCS) and the abolition of ACTH-induced increase in 17 OHCS and decrease of eosinophiles. Plasma volume, Na+, K+, and blood pressure and heart rate were unaltered. After two weeks of treatment with o,p'-DDD the dogs were anesthetized for pharmacological evaluation. Blood pressure and heart contractile force and rate responses to graded doses of epinephrine and norepinephrine were determined in treated and in untreated dogs. As a final test, cardiac contractile force response to ouabain was determined.