This study reports the distribution of two major tuber proteins, patatin and the 22-kilodalton (kD) protein and their mRNAs, in developing potato plants grown in the field under two diverse locations. Patatin was present at the highest levels in root tissue of all cultivars examined, excluding tubers. Root patatin mRNA accumulated from 10 to 20% of that of tubers. Patatin levels varied in leaf and stem tissue, depending on the cultivar and developmental stage. The banding pattern of the root and stem patatin proteins resolved on SDS-polyacrylamide gel electrophoresis was distinct from the tuber form, while the patatin transcript detected in root and stem mRNA from these tissues was approximately the same size as the tuber transcript. The 22-kD protein was detected in roots, stems, and leaves with slight quantitative differences among cultivars. Excluding tubers, the greatest and most consistent levels of this protein type occurred in leaf tissue. It was concluded that both tuber proteins can be expressed to detectable levels in nontuber tissues and that levels of accumulation seem to be affected by genotype (cultivar) and environmental factors, as well as stage of development.