A comparison of the behavioural peculiarities of Ixodes persulcatus Schulze, 1930 (north-western population, Russia) and Ixodes ricinus (L., 1758) from western Russia and Denmark was determined by using two methods. Method 1 involved a sojourn of ticks on vertical plastic sticks and showed that the questing behaviour of I. ricinus nymphs was dependent on temperature and relative humidity (RH). A significantly greater number of nymphs quested at 22 degrees C and 100% RH than at 18 degrees C. When the humidity was reduced to 30% all of the nymphs departed. In the second method, the activity of ticks on an inclined "ticksdrome" was estimated. The activity of I. ricinus adults from the Danish population was 1.2 times greater than that of ticks from Russia. Females of the species studied and specimens from all study areas were more active than all other stages of development. The locomotor activity of both adult and immature I. ricinus that were infected with Borrelia burgdorferi sensu lato was suppressed when compared with uninfected specimens. The locomotor activity of I. persulcatus females infected by borreliae with exoskeleton anomalies was 1.3 times greater (P<0.05) than that of infected ticks without anomalies. Our data showed that infected females with exoskeleton anomalies could crawl faster on a human and reach uncovered parts of the body that are vulnerable for attachment and feeding. A study of locomotor activity and questing behaviour may be useful for comparing the risk for different tick species and populations to transmit tick-borne pathogens.