A group of subjects of Bangladeshi adults from both sexes were studied for internal radioactivity and effective dose by measuring the whole-body activity of naturally occurring 40K using a whole-body counter. The mean activity concentration in the whole body and effective dose due to naturally occurring 40K for the average male were found to be 2.0 +/- 0.4 Bq x g(-1) and 100 +/- 26 microSv x y(-1), respectively and those for the average female were 1.7 +/- 0.3 Bq x g(-1) and 100 +/- 20 microSv x y(-1), respectively. The mean activity concentration in the whole body and effective dose for both sexes were 1.9 +/- 0.4 Bq x g(-1) and 100 +/- 25 microSv x y(-1), respectively. The effective dose from 40K for subjects is below the value reported by the UNSCEAR.