Effects of oral and intramuscular exposure to 1-naphthyl-N- methylcarbamate (63252) (carbaryl) on the learning activity of five young male Macaca-fascicularis-monkeys were evaluated. The monkeys were required to press four buttons in a specific sequence that was changed daily. All monkeys were tested several times at each carbaryl concentration. Baseline session time averaged 21 minutes and the mean number of errors was 33. After intramuscular injections of 1, 3, 5, and 10 milligrams per kilogram (mg/kg) carbaryl, mean session times were 22, 25, 36, and 54 minutes, respectively, and mean errors were 40, 44, 58, and 42, respectively. The error decrease following 10mg/kg injections probably resulted from a testing delay of 10 to 30 minutes. The error increases after 1 and 3mg/kg were 53 and 63 percent, respectively, but were not statistically reliable. Statistically reliable results were obtained after 5 and 10mg/kg injections when there was a 75 percent increase in errors over the control day. Oral administrations of dosages from 5 to 50mg/kg produced inconsistent effects. The authors conclude that monkeys are reliably affected by intramuscular injections of 5mg/kg carbaryl. This learning task is not recommended for determining the lowest effective concentration of a chemical unless an acquisition decrement is the major expected effect or the behavior of interest.