In the laboratory experiments, the virophoric period in D. marginatus ticks lasted 61 to 81 d, the premoulting period (nymphs - adults) amounted to 17 to 18 d. The titres of individually examined females and males for the presence of TBE virus ranged from 10(1) to 10(5.5) ic mouse LD50/0.03 ml between the 14th and 29th day after hatching. In the laboratory experiments 77% of ticks were positive. In the field experiments, the virophoric period in D. marginatus ticks lasted 79 to 114 d, the premoulting period amounted to 34 to 38 d. The titres of individually examined adults for the presence of virus ranged from 10(1) to 10(5.5) ic mouse LD50/0.03 ml between the 13th and 80th day after hatching. In the field experiments 96.5% of ticks were positive.