We evaluated the prevalence of hypertension and the age-related behaviour of systolic blood pressure (SBP) and diastolic blood pressure (DBP) in a wide sample of male and female Ethiopian Oromos living in rural or pre-industrial urbanized settings. Blood pressure (BP) was measured in the sitting position after 5 min rest in 5277 Oromos. In the group, 4928 were semi-nomadic shepherds, while 349 came from a town of 60,000 inhabitants where they were involved in low-technology jobs. The first subgroup was composed of 2482 men and 2446 women. All subjects were divided into 3 age groups: 15-44, 45-64, and > or = 65 years. Body weight (BW) and the Quetelet index (QI) were matched to BP levels using Pearson's method. In semi-nomadic men, SBP was 121.4 +/- 8.4 mmHg versus 132.4 +/- 10.4 mmHg in urban men (p < 0.001). In women, SBP was 120.5 +/- 7.9 mmHg versus 128.1 +/- 10.1 mmHg (p < 0.001). The prevalence of hypertension was 0.40% in the semi-nomadic and 3.15% in the urban population. In the latter, significant increases in BW and QI were found, which were significantly correlated to both SBP and DBP. In semi-nomadic men, a 5.33% increase in SBP and a 5.22% in DBP was found between age groups 1 and 2 (p < 0.001 in both). In urban men the increase was 4.77% and 3.41% respectively (p < 0.001). In both male populations no difference in SBP and DBP was observed between age groups 2 and 3.(ABSTRACT TRUNCATED AT 250 WORDS)