Traces of hazardous hydrocyanic acid that is formed during combustion of some nitrogenous compounds in cigarettes were determined by absorption in 1N sodium hydroxide, followed by potentiometric titration with 0.1N silver nitrate using an iodide-selective electrode. A programmable calculator was very convenient for calculation of the results which are based on evaluating the equivalence volume of the titrant from the point at which the second derivative D2E/DV2 becomes zero. The first end point is represented by the reaction Ag+ + 2CN - --> [Ag(CN)2] and the second end-point by [Ag(CN)2] - + Ag +-->2AgCN.When the first equivalence point was titrated NAg+ Ve = N CN- VCN- NCN- = MAg+ Ve/2VCN- WCN- = MAg+ VeEVo/2VCN- x 109 (µg). Where MAg+ and Ve are the molal concentration and volume of the equivalence point of standard silver nitrate. E is the molecular weight of hydrocyanic acid. VCN- and Vo are the volumes titrated and total volume of absorbing solution of hydrocyanic acid in smoke. This method is simple, rapid and sensitive. Recoveries were in the range 98,44 - 103,5%. The results of the determination of hydrocyanic acid in smoke for 12 kinds of cigarettes were in the range 15,0 - 45,3 (± 0,47) µg/cigarette and are in agreement with other reported methods of analysis .