Soil and tissue tests are important in determining the N status of soils and plants. Unfortunately, there are no leaf or soil tests recommended by the Extension Service in Louisiana for determining the N status of cotton soils or plants. A project was developed to determine the leaf N concentrations of the uppermost, fully mature, leaf blade best associated with N deficiency in cotton for Louisiana and Mid-South cotton. Nitrogen-rate fertilizer field experiments were conducted at 12 research station and farm sites in Louisiana, Arkansas, Mississippi, and Alabama in 1996. Some of the results were used to determine the critical value for leaf-blade N. Results indicated the leaf-blade total N % associated with N deficiency in cotton were at concentrations less than the values listed below: at 1^st pin-head square 5.2% N; at early-bloom 4.4% N; at mid-bloom (3 weeks after early bloom) 3.3% N; and at cut-out 3.3% N. These critical values were developed with incomplete data and will be modified depending on the outcome of the complete data set of 1996 and forthcoming 1997 results.