This article reports on the effect of dietary modification on changes in eating patterns and serum lipids among hypercholesterolemic persons aged 40-59 years with no evidence of coronary heart disease in Mae Sot District, Tak Province, between 1995 and 1996. A total of 381 persons with total cholesterol levels > or = 240 mg/dl and triglyceride levels < 400 mg/dl were educated, counseled, and followed-up by the mobile health team at the health centres in the communities. The team comprised both hospital personnel (a physician, a health educator, and public health nurses) and the health centre workers. Of the 381 study persons, 331 (86.9%) completed the one-year follow-up. The participants at one-year follow-up were more likely than at baseline to reduce intakes of dietary fat and cholesterol, whereas, there was an increased intake of vegetables and fruits. The mean total cholesterol level significantly decreased from 258.9 mg/dl at baseline to 236.1 mg/dl at one-year follow-up (p < 0.01), giving an 8.8 per cent reduction. The mean change in low-density lipoprotein cholesterol levels was a 26.0 mg/dl decrease (p < 0.01), yielding a 15.1 per cent fall. The mean high-density lipoprotein cholesterol level increased from 44.6 mg/dl at baseline to 46.8 mg/dl at one-year follow-up (p < 0.01). The proportion of those who had a body mass index of < 25 slightly increased from 70.7 per cent at baseline to 72.5 per cent at one-year follow-up. The dietary intervention program by the mobile team may be useful for lowering serum cholesterol among the rural population with hypercholesterolemia.