Obesity is a serious health problem worldwide and many genes have been implicated in determination of obesity, but our knowledge of the genes responsible for individual differences in weight loss after physical intervention are poor. One of the candidate genes is a gene for angiotensin-converting enzyme (ACE) ant its insertion/deletion (I/D) polymorphism. We have analyzed the association between the ACE gene variant in intervened obese females. Twenty four unrelated healthy obese (BMI > 29.9 kg/m(2), with abdominal type of obesity) premenopausal (age between 25 and 45 years) Czech Caucasian sedentary and non-diabetic females, pre-selected according the ACE I/D polymorphism (twelve II and twelve DD homozygotes) were studied in a medical research centre. They underwent 9 weeks intervention program (combination of the lowering of dietary intake to optimal level for the age and 3 times a week physical activity at fitness centre). The participants were supervised to sustain a heart rate of 65 % of maximum. Anthropometrical, biochemical parameters and body composition (Bodystat 1500) were analyzed before and after the intervention. Our study suggest, that in Czech Caucasian females I/D polymorphism within the ACE gene will have no major effect on weight loss. Interestingly, we have detected, that in obese females II genotype was associated with higher increase in basal metabolic rate (202 kcal per day) then in DD homozygotes (p<0.05), thus at least under some circumstances, this genetic variant may have an slight effect on BMI development.