It is known that by the reaction of chlorine added to drinking water for disinfection with humic material, organochlorine compounds are formed. Of them, more than 90% are high molecular weight organochlorines and about 10% are chloroform, dichlorobromomethane, dibromochloromethane and bromoform which are in short called trihalomethanes, THM＇s. These are wellknown for their carcenogenic activities; Thus research is being continuously performed on their formation and determination. In this report we measured the total trihalomethanes, TTHMs, present in drinking water of Ondokuz Mayis University and the City of Samsun in the year of 1992. For the analysis we used a gas chromatograph equipped with an electron capture detector. The total amount of THM＇s content of all analyzed drinking water samples seems to he below the limit values accepted by USEPA. However, they are still much higher than the THM＇s found in the drinking water of various countries.