Nicotine was determined by a reagent-injection flow injection photometric method making use of the Koing reaction. The applicability of four color reagents, aniline, barbituric acid, pyrazolone and sulfanilic acid, were evaluated and the sulfanilic acid was selected. The linear range, detection limit, R.S.D., and sample throughput of the established sulfanilic acid method were 0-10 mg l(-1), 0.12 mg l(-1), 0.7% and 50 h(-1), respectively. Background absorption from sample matrix was eliminated by the reagent-injection flow injection technique. The proposed method was applied to determine nicotine in tobacco and urine samples with satisfactory results.