The Swedish trial in old patients with hypertension (STOP-Hypertension) is a multicentre, randomized, double-blind study of beta-blockers/diuretics versus placebo in old hypertensives. Primary end-points are stroke and myocardial infarction (fatal and non-fatal) as well as other cardiovascular mortality. To evaluate the logistics of STOP-Hypertension, a pilot study was carried out. All patients aged 70-84 years in 31 centres were consecutively registered in a log-book. Altogether 4668 patients were screened: 41.5% had previously been treated for hypertension and 13.5% had blood pressures greater than or equal to 180/105 mmHg. Thus, 55% were 'hypertensive'. In all, 465 patients (18% of the 'hypertensive' patients) started a 3-month washout period (previously treated, n = 396) or a 4-week run-in period (previously untreated, n = 69) period. The most frequent reasons for not starting the run-in/washout were other indications for treatment with beta-blockers/diuretics (13%), unwillingness to participate (8%) or isolated systolic hypertension (4%). The pilot study was evaluated after 1 year: 89 patients (1.9%) had been randomized, 66 patients (1.4%) were still in the run-in/washout period and the majority of the remaining patients were not randomized because they had not reached the inclusion blood pressure (greater than or equal to 180 mmHg systolic and/or greater than or equal to 105 mmHg diastolic) following withdrawal of their antihypertensive medication. During the run-in/washout period there were few serious clinical events: one case of myocardial infarction, three patients had strokes (two fatal), 10 developed congestive heart failure, three tachyarrhythmia and two pneumonia (one fatal).(ABSTRACT TRUNCATED AT 250 WORDS)