ow and stable level of BP, and may decrease the risk of adverse events, including stroke and heart failure. Therefore, it is important to understand the factors that regulate the fluctuation of BP. Temperature is suspected to be one of these factors, and several studies have suggested the association of fluctuation of BP with seasons or ambient temperature. However, most were cross-sectional studies or follow-up studies with few repeated measurements. Except during pregnancy, it is unclear whether and to what level, systolic blood pressure or diastolic blood pressure, or both, change with temperature in long-term longitudinal studies. Also, it is unclear whether regulators of hypertension, such as age, smoking behavior and antihypertensive medication, modify the association of BP and temperature. The aim of the present research is to investigate the association between BP and ambient temperature, and further explore potential factors that would modify this association. It is based on a three-year surveillance of 1,831 hypertensive patients with 62,452 repeated measurements. Materials and Methods Ethics Statement This study was approved by the institutional review boards of Peking University. All subjects provided written informed consent. Study Design and Participants The research is a secondary analysis 
of a longitudinal study with 3-year follow-up of 1,831 hypertensive 26148857 patients, which was a part of the Chinese Community-based Comprehensive Prevention and Control of Hypertension, a project consisting of 34,770 permanent residents over 35 years old in the Nanshi District, Shanghai, China. The subjects were recruited from a census of BP in the residents from June, 1997 to April, 1998. In brief, among the 34,770 participants, those with mean BP$140/ 90 mmHg or current use of antihypertensive medication were defined as hypertensive patients, After exclusion of patients with severe morbidity, 1831 patients with written informed consent were recruited into the three-year surveillance of BP. Urine samples Ambient Temperature, Blood Pressure and Regulators were collected for clinical examinations including urine protein analysis. Baseline information including age, sex, BMI, and lifestyle, was obtained by a questionnaire. Patients were asked to come back to the clinics of their community for interview every 2 to 4 weeks. During baseline and the following interviews, BP was measured in the right arm of seated participants after a 5-minute rest by mercury sphygmomanometer with appropriately sized cuff. Measurement was performed at three 1-minute intervals according to standard protocol. The mean of the three measurements was calculated as the record of BP. At each visit, benazepril hydrochloride, a type of angiotensin converting enzyme inhibitor was prescribed for all patients and the drug dose was adjusted in the first 8 weeks according to whether the participants’ BP was below 140/90 mmHg; a small proportion of patients also received dihydrochlorothiazide. Additional details of study design were reported elsewhere. The average baseline blood pressure of the study population was 149.0/93.4 mmHg right before 518303-20-3 prescription of benazepril. At the two-week’s follow-up, patients’ BP dropped to 142.9/89.9 mmHg. Since the fourth week, BP declined slowly to 133.2/82.1 mmHg at the 156th week. At the 156th week, 72.5% of the patients 14557281 remained in the study, with an accumulation of 62,452 follow-up records, of which 60,463 were at the fourth week and after.