This study investigated the optimal time for measuring stress and immune function in 20 healthcare professionals (19 women and 1 man) following interaction with a therapy dog. A nonclinical sample of healthcare professionals was assigned to 20 min. of quiet rest, and 5 and 20 min. with a therapy dog. Serum cortisol, epinephrine, and norepinephrine were collected at baseline, 5, 15, 30, 45, and 60 min. postcondition. Salivary cortisol, salivary IgA, and blood for lymphocytes were collected at baseline, 30, 45, and 60 min. postcondition. Analysis indicated significant reductions in serum and salivary cortisol. The optimal time for measuring serum or salivary cortisol following interaction with a therapy dog was 45 min., with changes in salivary cortisol reflecting serum cortisol changes. Findings also suggest stress reduction in healthcare professionals may occur after as little as 5 min. of interaction with a therapy dog and warrants further investigation.