OBJECTIVE To compare ambulatory blood pressure recorded during a work day with a leisure day regarding masked hypertension. DESIGN A randomized crossover study in middle-aged normotensives. PARTICIPANTS Thirty-seven untreated middle-aged normotensives (17 women), who had repeated office blood pressure less than 140/90 mmHg. MAIN OUTCOME MEASURE Individual difference of masked hypertension between a work day and a leisure day. RESULTS Office systolic/diastolic blood pressure mean (SD) was 0.3/0.6 (6.4/5.2) mmHg higher during the work day. The mean (SD) systolic/diastolic 24-h, day and night blood pressure was 2.8/3.1 (4.5/3.6), 2.2/2.5 (4.9/4.2) and 1.3/1.9 (4.6/4.0) mmHg higher during the work day than during the leisure day. Individual comparisons of occurrence of ambulatory blood pressure values above normal during day (systolic ≥135 or diastolic ≥85) showed a statistically significant difference between the work day and the leisure day, P=0.0412. The P values for the individual comparisons of occurrence of ambulatory blood pressure values above normal during 24 h (systolic ≥130 or diastolic ≥80), and during night (systolic ≥120 or diastolic ≥70 mmHg) were P=0.0771 and 0.6171, respectively. CONCLUSION Ambulatory blood pressure was somewhat higher during the work day than during the leisure day, and there was statistically significant individual difference concerning masked hypertension during daytime. Thus, in normotensives such as in hypertensives, ambulatory blood pressure during a work day seems to give the best information. Diastolic blood pressure values above normal were more common than systolic. However, systolic blood pressure is considered of greater importance in this age group and no participant had extremely high values.