A sequential Bayesian algorithm and accompanying computer program were developed and validated to estimate population numbers of adult blacklegged tick, Ixodes scapularis Say, using mark-release-recapture methodology in field plots in central Mississippi. In fieldwork, data taken in February 2005 in a 1-ha plot yielded an estimate of 317 adult I. scapularis per ha Data from another field plot in 2006, 3 km away, yielded an estimate of 280 adult I. scapularis per ha The number of ticks collected per hour in both plots averaged 4.5. In eight of 14 (57%) of sampling events, the number of ticks collected per hour hovered closely around 5.0 (4.8-5.3). The computer program developed in this study readily produced statistical measures such as mean number of ticks per plot, mode, variance, and standard deviation, as well as easy-to-read graphs of estimated tick populations for each sampling period.