Time trends and social factors in detection, treatment and control of hypertension in the community were examined in four independent Scottish MONICA cross-sectional surveys in 1986, 1989, 1992 and 1995. Residents aged 25-64 years were recruited randomly from general practice lists in north Glasgow, Scotland with stratification by sex and 10-year age groups. A total of 1262 participated in the first survey, 1397 in the second, 1516 in the third and 1836 in the fourth. Differences and trends in proportions of hypertension undetected, detected but untreated, treated but uncontrolled and controlled across the four surveys were tested by chi(2), and the associations of the poor control of hypertension with social factors were estimated by multivariate logistic regression model to derive odds ratios. Using the cut point of >/=160/95 mmHg, proportion of hypertension undetected across the four surveys was 56.3, 44.6, 32.0 and 38.2%, and of treated controlled hypertension was 15.2, 26.4, 32.0 and 32.8% (both trends P<0.001). Multivariate analysis showed that poor control of hypertension was not related to social deprivation, but significantly related to being male, young, of low body mass index and heavy alcohol drinking. Undetected hypertension was significantly related to full-time employment, and untreated hypertension to high social class and possibly education level. These findings suggest that in this part of Scotland the management of hypertension has improved, so the 'rule of halves' no longer applies. Control of blood pressure is not positively associated with social deprivation, but people at a high risk of poor control of hypertension should be targeted.