Prevalence and predictors of masked arterial hypertension (AH) in patients receiving antihypertensive therapy (concealed treatment inefficacy--CTI) was studied on material of data base comprising 219 observations. Drugs from 5 groups were used. Prevalence of CTI AH with the use of various definitions was 8.1-17.4%. With the help of procedure of logistic regression analysis the following predictors of CTI were selected: (1) sociopsychological--high working capacity, high psychological abilities and social self feeling; (2) parameters of 24-hour BP profile--24-hour variability, variability during working period, minimal daytime BP level, time of maximal BP. According to our data CTI is most probable during treatment with calcium antagonists and beta-adrenoblockers.