We examined the validity and accuracy of telepathology service in the histological diagnosis of biopsy specimens from human transplanted kidney and liver. The still video images of paraffin sections were transmitted via a two-way telephone by use of a digitized telephone network (Integrated Service Digital Networks, 64 kbits/sec). The images were displayed on monitors and diagnosed by an expert pathologist at Tottori University. The quality of transmitted still images was sufficient for the diagnosis, especially at higher magnifications. The average number of transmitted images was 6.2 in the kidney cases and 7.4 in the liver cases. The average time taken for examination of a case was 13 min (range 10 to 16 min). Of 12 biopsy specimens from transplanted kidneys, 10 were adequately diagnosed with the system. Sampling errors caused inadequate diagnosis in a case of cyclosporin tubulopathy, the still images of which were not transmitted. An expert pathologist rendered the diagnosis in a case showing mesangial sclerosis, which was later diagnosed as possible recurrent glomerulonephritis through direct microscopy. Biopsy specimens from 10 liver transplants were also tested using archival materials. Although the etiology of hepatitis could not be determined in one case, diagnoses by telepathology well agreed with the reported diagnoses made through direct microscopy. Telepathology may be an effective way to provide on-line consultations in transplantation pathology, especially for transplant teams lacking expert pathologists.