We continuously recorded the activity of adult and nymphal blacklegged ticks, Ixodes scapularis Say, exposed to diurnal light and temperature cycles in a laboratory test chamber by using a digital camera controlled by an intervalometer. Adult ticks collected and tested in the fall exhibited a bimodal pattern of activity, with peaks shortly after lights on and shortly after lights off, and substantial daytime activity. However, adult ticks collected in the winter and early spring exhibited a unimodal pattern of activity, peaking shortly after lights off, and minimal daytime activity. Nymphs, collected and tested in the summer, exhibited only a unimodal pattern of activity, peaking after lights off. Limited data also are presented for adult ticks exposed to only a temperature cycle or to only a light cycle in the spring. Ticks exposed to a temperature cycle exhibited a unimodal pattern of activity, similar to that exhibited by ticks exposed to both light and temperature cycles at the same time of year, whereas those exposed to a light cycle exhibited a bimodal pattern of activity. Although the difference did not quite reach statistical significance, there is a possibility that temperature is a stronger entraining agent for tick diurnal activity than is light, an unusual situation. The change in diurnal activity pattern from fall to spring suggests that ticks are adjusting their strategy for host finding, possibly in relation to remaining stored food supplies or host activity, and may have practical implications for sampling carried out to track tick populations.