CASE PRESENTATION: A 51 year-old non-smoking woman (CR) presented with worsening dyspnea over six months. She swims indoors and uses a sauna but no hot-tub. Dyspnea was present on level ground with dry cough. Basilar rales were present. PFT: mild airway hyper-reactivity, normal lung volumes, no gas trapping and DLCO 52%. CT revealed diffuse HP. Rapid decline occurred. Open biopsy confirmed acute hypersensitivity, no AFB seen. Prednisone 1mg/ kg resulted in clinical response. M. avium (MAC) grew from the biopsy and triple anti-NTM therapy was added as a prolonged prednisone course was anticipated. Pool and sauna avoidance was initiated. Prednisone was tapered as symptoms subsided, CT cleared, DLCO normalized. Sputum sterilized at eight months of treatment. She has returned to swimming but not to the sauna. The patient's 65 year old non-smoking husband (CF) presented two months later with four months of progressive dyspnea. PFT: Mild obstruction and normal DLCO. CT showed centrilobular ground glass nodules and subacute HP diagnosed. Sputum grew MAC x 3. Symptoms and CT resolved with sauna avoidance in four months. Sputum cultures remain positive. Home water specimens were analyzed by PCR fingerprinting methods. (J.Falkinham lll, PhD). Table I. Pool and sauna samples were not available for testing. Each household member had a different PCR Type, matching different water sources in the home. No intervention has been made in home water sources.