Early and late peanut leaf spot caused by Cercosporaarachidícola S.Hori and Cercosporidium personatum (Berk. & M.A. Curtis) Deighton, are responsible for major yield losses in peanut (Arachis hypogaea L.), in the productive areas of Córdoba province- Argentina. Environmental conditions that favor the diseases have already been described by different authors and peanut production areas. In Córdoba, Argentina, leaf spot disease development was related to air temperature and relative humidity measured at the canopy level. The objective of this research was to get a better insight into the relationships between routinely measured weather variables and peanut leaf spot development, for operative prediction purposes. Experiments were conducted on farmer peanut fields close to Río Cuarto, Córdoba-Argentina (33°07' S Latitude, 64°14' W Longitude, 421 m above see level), and on the Agricultural Experimental Station of the University of Río Cuarto (UNRC). Weekly data for peanut leaf spot incidence obtained from the experimental sites were provided by the Plant Pathology Area of the UNRC, for five peanut crop seasons (1986/87 to 1990/91). Identical determinations were done during the 1997/98 peanut crop season. Weather data were collected from closest stations to the experimental fields. Daily maximum and minimum air temperature, relative humidity and rainfall data were analyzed and accumulated on a weekly basis throughout the crop cycle. Derived meteorological variables related to disease development were generated. Disease incidence curves showed not only differences in the date of initiation of the disease infection but also in the rate of progress, for each of the crop seasons. A Stepwise procedure was applied to select significant variables contribution to the disease incidence. Weekly cumulative hours with relative humidity >80% and weekly cumulative rainfall along the crop season, in a linear regression model explained 92% of the variability in the disease incidence. The RMSE between the observed and predicted values of disease development was 8.8 % and 12.4 %, for two independent generated leaf spot data sets