Twenty obese patients, two males and 18 females, with a mean (± SEM) age of 41.7± 3.2 years and body mass index (BMI) of 31.8± 3.8 kg/m2, were enrolled in a 16-week study to evaluate the usefulness and limitations of treatment with a sweet basil seed (Ocimum canum, Sims) extract. For 16-week (wk0-wk16), they were instructed to reduce their usual energy intake. After baseline observations for 4 weeks, for 12 wk (wk4-wkl6), patients were asked to ingest 2 g of sweet basil seed extract, swollen with 240 ml of water, before lunch and supper (4 g/day). Sixteen patients commenced extract use at wk4. On the basis of their ability to ingest more or less than 50% of the extract, they were categorized into high dose (n= 10) and low dose (n=6) users. In high dose users, there were a significant decrease in BMI by the 4th week of treatment which was maintained at the 8th and 12th weeks of treatment, but skinfold thickness measurements for fat did not decrease. There may, therefore, have been a reduction in total body water. Further support for this view was provided by an observed increase in serum total protein concentration at the 12th week of intervention. That the distribution of water may have changed was suggested by an increase in upper arm muscle circumference (UAMC). For low dose users, on the other hand, their body fat increased at wk8 as indicated by both BMI and skinfold thickness measurements, suggesting that supplement use gave a sense of false security. Apart from the change in serum total protein in the high dose group, no significant effect was observed on lipid, renal or electrolyte status, although fasting glucose rose within the normal range. This investigation demonstrated the importance of direct measures of body fatness, as opposed to those implied from weight-height relationships in the evaluation of management strategies for obesity.