A novel simple kinetic spectrophotometric method for the determination of N-acetyl-L-cysteine (NAC) has been developed and validated. The proposed method is based on a coupled redox-complexation reaction, the first step of which is the reduction of Fe(3+) by NAC; the second one includes the complexation of Fe(2+), resulting from the preceding redox reaction, with 2,4,6-trypyridyl-s-triazine (TPTZ). The stable Fe(TPTZ)(2)(2+) complex exhibits an absorption maximum at lambda = 593 nm.The initial rate and fixed-time (at 5 min) methods were utilized for constructing calibration graphs. The graphs were linear in concentration ranges from 4.0 x 10(-6) to 1.0 x 10(-4) mol L(-1) for the initial rate method and 1.0 x 10(-6) to 1.0 x 10(-4) mol L(-1) for the fixed-time method, with detection limits of 1.0 x 10(-6) and 1.7 x 10(-7) mol L(-1), respectively. The proposed methods were successfully applied for the determination of NAC in its commercial pharmaceutical formulations.