The purpose of this study was to utilize a mobile phone for transferring medical images to a specialist at a remote site in emergency care. CT images obtained in emergency treatment are transmitted via the Internet or mobile phone (CDMA: Code Division Multiple Access communication method). A specialist even at a remote mobile site may receive the appended images of e-mail sent via mobile phone to his PDA (Personal Digital Assistant, image indicator). The images are originally obtained in DICOM format by CT, and are then converted to JPEG format. To reduce transmission time, the JPEG files can be compressed without causing undue deterioration in image quality. To evaluate the quality of images received at the remote site, images were compressed at 25, 40, 50, 60, 70 and 80% compression ratios and transmitted to a PDA via the Internet and a mobile phone or a mobile phone alone. Image quality was visually evaluated by BVC analysis. The analysis revealed that the image compression ratio must be at least 50% for diagnosis. Considering the transmission speed, a 50% compression ratio was considered the most suitable for this application.