The midsummer seasonal decline in abundance of unfed Ixodes scapularis Say nymphs on experimental plots in New Jersey was density-dependent. Nymph density was manipulated on 9 plots (10 by 10 m each) in Morristown. National Historical Park, NJ, in early June 1994. Subsequent rates of decline were directly proportional to initial density (linear regression, R2 = 0.83). A 6-fold manipulation of density caused more than a 10-fold increase in per-capita disappearance rate. Absence of density-dependent mortality in simultaneous field cage experiments implicated dispersal at rates higher than reported previously, positive-density-dependent host finding success, or predation, possibly in the form of host grooming. Each of these possibilities has important implications for the role of unfed nymphs in the regulation of I. scapularis populations.