INTRODUCTION In October of 1970@ the blood sampling phase of the research study ' to determine the range of carboxyhemoglobin (COHb) in various segments of the American population was formally initiated when sample collections began in cooperation with the Milwaukee Blood Bank. In the ensuing weeks@ a plan for the efficient sampling@ handling and shipping of samples of blood and breath was put into operation. An efficient data gathering and processing system was formed to insure efficient storage and easy retrieval of data for subsequent data analysis. Over the past 12 months@ approximately 17@ 500 blood samples and over 1@ 000 breath samples were collected from blood donors at 13 major sampling locations throughout the nation. Two of these locations were re-visited@ so that a total of 15 separate sampling programs have been conducted. The success of the project depends not only upon collection of samples@ but upon the ability to analyze those samples@ rapidly and with accuracy and precision. Methods used initially for the analysis of CO in blood@ breath and air have undergone continual critical review and improvement. The study design described in the initial protocol has been adhered to with only a few minor exceptions. Two of the sampling locations listed on the protocol@ Los Angeles and Salt Lake@ have not been visited; however@ both of these cities will be worked into Phase II of the sampling program. In general@ the program has been well received and the goals for the first year of sampling adequately attained. Samples collected from the Milwaukee area before the initiation of the COHb Mass Screening Program have been combined with those of the regular Milwaukee study to form a detailed written report. At this writing@ data from five other cities@ New York@ Miami@ St. Louis@ Chicago and Washington@ D. C. have undergone preliminary computer analysis. A manual analysis of lab tabulated data has also provided up-to-date information on non-smokers for all of the sampling sites and cities thus far visited. The extent and location of sampling to be conducted over the final year of the survey will be dictated somewhat by the results of the preliminary analysis of segments now completed. Additional samples needed for completing certain population segments for race@ sex@ age@ etc. will require that some cities be re-visited while an effort will also be made to increase the sample size of groups having special occupations {e. g. @ firemen@ taxi cab drivers@ housewives)@ or other distinguishing characteristics (e.g.@ hospital inpatients@ newborn infants@ expectant mothers).