A system has been developed which uses an imaging-plate diffraction apparatus to obtain structure factors for protein crystals. The latter is connected to a graphics workstation through an Ethernet. Pixel data from an imaging plate are transferred via the Ethernet to a workstation and processed to give the structure factors. The quality and precision of the diffraction data were examined from the point of view of spatial uniformity, linearity with exposure, decay with time, and reproducibility. X-rays from an 55Fe source and Debye-Scherrer rings from Si powder were used for calibration purposes. Finally, diffraction data were obtained and evaluated for lysozyme and cytochrome c-553 using this system. The results were satisfactory in terms of sensitivity and precision.