This study was conducted at two sites in Mississippi to determine whether petiole and leaf NO‐3monitoring could be used as a management tool in making fertilizer N recommendations for sunflower (Hellanthus annuusL.). Petiole and leaf samples were taken at the four leaf stage at both sites, and later at two week intervals at Brooksville. Petiole and leaf NO‐3at the four leaf stage was significantly influenced by rate of N application at both sites. The level of petiole and leaf NO‐3was highly correlated with rate of N application as well as with seed yield. The concentration of NO‐3in petioles and leaves was greatest at the four leaf stage and showed quadratic declines as the season progressed. Petiole and leaf NO‐3showed the highest correlations with rate of N application and seed yield at the four leaf stage than at any other sampling time at Brooksville, indicating that this was the “best” period for taking petiole and leaf samples. However, analysis of petioles and leaves at the four leaf growth stage for NO‐3may have limited potential of becoming a useful tool in making N fertilizer recommendations for sunflower. This is due to the sensitivity of both petiole and leaf NO‐3to time of sampling and locational differences, as well as lack of information on response of sunflower to N applied after this stage of growth.