This report describes the results obtained and data analyses from an interlaboratory evaluation of EPA Method 607 (Nitrosamines). The method is designed to analyze for three nitrosamines, N-nitrosodimethylamine, N-nitrosodi-n-propylamine, and N-nitroso-diphenylamine, in water and wastewater. The study design required the analyst to dose six waters with each of six mixtures of the three nitrosamines. The six dosing levels represented three Youden pairs, one each at a low, an intermediate, and a high level. A total of 17 laboratories participated in the study. The method was studied to estimate the accuracy and precision that can be expected, including effects on the accuracy and precision of analysis of different matrices. In addition, results of method detection limit and analytical curve studies and qualitative assessments of the method based upon comments by the participating laboratories are included.