The objective of the present study was to determine the acetylator status of the Bangladeshi population and to compare the findings with the acetylator status of other Asian populations. The acetylator phenotype was determined in 517 unrelated healthy Bangladeshi subjects. The phenotyping procedure was done according to Price Evans' method using the NAT2 specific probe drug--sulphadimidine. The Bangladeshi population showed a bimodal distribution of fast and slow acetylators. Of a total of 517 healthy Bangladeshi, 79.5% (n=411) were fast acetylators and the rest 20.5% (n=106) were slow acetylators. The high frequency of the fast acetylators in the population of Bangladesh was comparable to other populations in East Asia. When this acetylator status was compared with other Asian data, the Asian population showed a positive correlation between the acetylator status and the geographical longitude (r=0.919; t=7.37; p>0.001; d.f.=10). The regression line of the scatter diagram showed that the frequency of acetylating capacity increasingly occurred in the populations towards eastern Asia (regression coefficient=0.54; constant=52.36). This line was termed as the Asian fast acetylator longitude (AFAL). Thus the AFAL was able to predict the acetylator status of the Asian population by the east-west geographical longitude. The AFAL could be a useful prognosticator in the disposition for the effective and safe use of numerous drugs and xenobiotic compounds in humans.