The aim of this work was to study morpho-functional myocardial characteristics in patients with masked arterial hypertension (AH) and white coat hypertension (WCH) given antihypertensive therapy (AHT) and without it. This cross-sectional cohort study included employees of a large industrial enterprise who annually underwent routine medical examination supplemented by 24 hr AP monitoring and echocardiography carried out at specified time of the working day. The participants of the study were divided into 6 groups based on the relationship between clinical AP and mean AP during work. Group I comprised 20 (7%) subjects with normal AP, group 2--20 (7%) with masked AH, group 3--40 (14%) with WCH, group 4--81 (28.3%) with optimal A HT effect, group 5--64 (22.4%) with unmanifest inefficiency of AHT, group 6--40 (14%) with WCH during AHT. Criteria for masked AH and unmanifest AHT inefficiency were clinical AP below 140 and 90 mm Hg in combination with mean AP during work 135 and/or 85 mm Hg and higher. Echocardiography was performed in a standard positions in M- and B-modes as well as in three Doppler regimes. One-factor ANOVA was used to analyze differences between the groups and Pearson's Chi-square test to determine the relationship between categorical variables. 206 (72%) of the 286 employees of the large industrial enterprise had a diagnosis of AH. It was shown that ambulatory AP values obtained by 24 hr monitoring better characterized the patient's condition than clinical AP since they correlated with the frequency of disorders in the target organs and the risk of cardiovascular complications in patients with AH. Patients with masked AH more frequently developed left ventricular hypertrophy and diastolic dysfunction than those having normal clinical and ambulatory AP. The mean width of the left ventricle wall and left ventricular isovolumic relaxation time (therefore, the degree of LV hypertrophy and diastolic dysfunction) in the patients with unmanifest inefficiency of AHT were greater than in those with optimal AHT effect. The occurrence of WCH was comparable in the two groups. These data were used to determine intensity of preventive AHT at the workplace with a view to improving medical and occupational prognosis.