Background: Magnifying endoscopy is a promising modality for fine observation of minute surface structures and microvessel architecture in gastric lesions. Objective: To observe the response of microvessels to epinephrine stimulation in early gastric cancer tissues and to assess the usefulness of magnifying pharmacoendoscopy for histologic diagnosis. Design: This was a prospective pilot study. Setting: This study was conducted at an academic hospital. Patients: Twenty-nine patients with differentiated early gastric cancer were enrolled. Interventions: Microvessels in both the cancerous lesion and its adjacent non-neoplastic gastric mucosa were observed by magnifying endoscopy before and after focal spray with epinephrine solution (0.05 mg/mL).Main Outcome Measurements and Results: After epinephrine stimulation, noncancerous gastric mucosa surrounding the cancerous lesion showed a change in color from red to white; no microvessels were evident. On the other hand, all the cancerous lesions examined clearly showed enhancement of tumor microvessels. The rate of detection of tumor microvessels by magnifying pharmacoendoscopy (100%) was significantly higher than that by magnifying endoscopy alone (41.3%). Limitations: This was small pilot study. Conclusions: Magnifying pharmacoendoscopy with epinephrine is a powerful tool for assessing tumor vascularity and may contribute to the histologic diagnosis of differentiated early gastric cancers before endoscopic treatment. Background: Magnifying endoscopy is a promising modality for fine observation of minute surface structures and microvessel architecture in gastric lesions. Objective: To observe the response of microvessels to epinephrine stimulation in early gastric cancer tissues and to assess the usefulness of magnifying pharmacoendoscopy for histologic diagnosis. Patients: Twenty-nine patients with differentiated early gastric cancer were enrolled. Interventions: Microvessels in both the cancerous lesion and its adjacent non-neoplastic stomach mucosa After being exposed by magnifying endoscopy before and after focal spray with epinephrine solution (0.05 mg/mL). Main Outcome Measurements and Results: After epinephrine stimulation, noncancerous gastric mucosa surrounding the cancerous context: a change in color from red to white; no microvessels were Evident. On the other hand, all the cancerous lesio The valence of detection of tumor microvessels by magnifying pharmacoendoscopy (100%) was significantly higher than that by magnifying endoscopy alone (41.3%). Limitations: This was small pilot study. Conclusions: Magnifying pharmacoendoscopy with Epinephrine is a powerful tool for assessing tumor vascularity and may contribute to the histologic diagnosis of differentiated early gastric cancers before endoscopic treatment.