The Dictyostelium gene ampA, initially identified by the D11 cDNA, encodes a novel anti-adhesive-like protein. The ampA gene product inhibits premature cell agglutination during growth and modulates cell-cell and cell-substrate adhesion during development. Analysis of the promoter indicates that cap site-proximal sequence directs ampA expression during both growth and early development. Expression following tip formation is controlled by more distal sequence, which contains TTGA repeats known to regulate prestalk cell gene expression in other promoters. Comparison of reporter gene expression and endogenous mRNA accumulation indicates that during growth the ampA gene is expressed in an increasing number of cells as a function of density. The number of cells expressing the ampA gene drops as development initiates, but the cells that continue to express the gene do so at high levels. These cells are initially scattered throughout the entire aggregate. By the tip formation stage, however, the majority of ampA-expressing cells are localized to the mound periphery, with only a few cells remaining scattered in the upper portion of the mound. In the final culminant, ampA is expressed only in the upper cup, lower cup, and basal disc. Although reporter expression is observed in cells that migrate anteriorly to a banded region just posterior to the tip, expression is rarely observed in the extreme tip. AmpA protein however, is localized to the tip as well as to ALCs during late development. The results presented here suggest that ampA gene expression is shut off in ALCs that continue along the prestalk differentiation pathway before they are added to the primordial stalk.