Dates of the grape harvests in northeastern France and Switzerland exhibit significant correlations with the North Atlantic Oscillation (NAO), a large-scale mode of climate variability over North Atlantic. These correlations, established for the monthly values of the NAO index over the last 175 years, reveal characteristic signatures as a function of frequency. Conversely, these signatures may be used to test the robustness of existing NAO paleoreconstructions, thanks to the availability of harvest dates for northwestern Europe since the end of the fifteenth century. Climatic signal appears prevailing over possible human factors in these series. The results demonstrate the importance of including old instrumental data and of providing monthly values rather than annual means in the NAO reconstructions. They suggest that the available long harvest dates series could constitute an interesting proxy to constrain such reconstructions. ¿ 2001 American Geophysical Union