Lead is one of the most common metals in contaminated ecosystems. Although lead poisoning and mortality have long been known, little is known of the behavioral effects produced by low levels of lead in wild animals. Herein a 15-yr research program on the behavioral effects of lead using herring gulls (Larus argentatus) and common terns (Sterna hirundo), referred to as larids, as models is reviewed. The doses used in laboratory studies were sufficient to produce lead concentrations in feathers that were equivalent to those found in some birds living in the wild. The exposure consisted of a single or multiple intraperitoneal (ip) injection of lead acetate. Both dose and day of exposure influenced behavioral development in young larids, with most effects increasing with dose, and decreasing with age. Low-level lead affected growth, locomotion, balance, food begging, feeding, thermoregulation, depth perception, and individual recognition in laboratory and in wild birds. The accuracy of individual recognition was most affected by lead exposure from 2 to 6 d of age; exposure at 12 d did not affect accuracy, but it delayed response time significantly. Behavioral deficits observed in lead-injected young in the wild were similar to those observed in the laboratory, except that recovery was more complete by fledging than it was in laboratory-raised chicks. Further, parents in the wild were able to provision lead-exposed chicks sufficiently so that they fledged at similar weights as control chicks, a feat that is difficult to achieve in the laboratory. The lead-induced behavioral deficits observed in the laboratory and in the wild are sufficient to affect growth and survival in wild herring gulls. Lead treatment altered the expression of cell adhesion molecules (CAMs), which play a crucial role in the formation and deployment of neurons in the developing brain. The timing and sequencing of CAM expression is critical to normal development, and the different consequences of lead exposure at different ages may be related to interference at different points in the sequence.