The induction of acid pathogenesis-related proteins (PR-proteins) of group 1 (PR-1) by systemic virus infections of tobacco plants was investigated during a time period between 3 and 19 days after inoculation. Each leaf position was investigated separately. The PR proteins were detected electrophoretically and, in addition, virus protein was detected by Enzyme Linked Immunosorbent Assay (ELISA). Potato virus X (PVX) and potato virus Y (PVY) were found to highly induce PR proteins in N. tabacum L. “Samsun NN”. The same results were obtained when PVX was investigated in N. tabacum L. “Samsun”. The accumulation started later and took place more slowly than during hypersensitive host reaction (HR) of “Samsun NN” to tobacco mosaic virus (TMV). A correlation was found between the accumulation of PR proteins and the accumulation of the virus in the same leaf. Cucumber mosaic virus (CMV) was less effective in PR protein induction than PVX and PVY. Consequently it could be demonstrated that PR proteins do not only appear due to hypersensitive host reactions but also during systemic virus infections.