OBJECTIVE To determine the reference range for glucose tolerance, using a simplified glucose tolerance test (GTT), and to evaluate glucose tolerance status in cats. DESIGN Prospective study. ANIMALS 57 clinically normal cats. PROCEDURE 2 catheters were placed in the cephalic veins of nonsedated cats at least 3 hours before the test. Blood samples were obtained before (0 minutes) and 2, 5, 10, 15, 30, 45, 60, 90, and 120 minutes after glucose (0.5 g/kg [0.23 g/lb] of body weight) was injected i.v. Blood glucose concentration was measured by a glucose meter. Glucose half-life (t1/2) and disappearance of glucose (Kglucose) were calculated. RESULTS Glucose tolerance in cats was considered normal when upper limits for glucose concentration were < or = 159 mg/dl at 0 minutes, < or = 322 mg/dl at 60 minutes, < or = 238 mg/dl at 90 minutes, or < or = 171 mg/dl at 120 minutes and glucose t1/2 was < or = 94.7 minutes or Kglucose was > or = 0.41%/min. Impaired glucose tolerance in cats was defined as a glucose concentration > or = 160 mg/dl at 0 minutes, > or = 323 mg/dl at 60 minutes, > or = 239 mg/dl at 90 minutes, or > or = 172 mg/dl at 120 minutes. The frequency of impaired glucose tolerance was 2%. Five cats had stress-affected GTT. Significant differences in glucose t1/2 or Kglucose between cats < 7 and > or = 7 years old were not found. CLINICAL IMPLICATIONS The simplified GTT and measurement of glucose concentration by a glucose meter provides a simple and low-cost method of assessing glucose tolerance status in cats that are normoglycemic after food is withheld. Use of absolute glucose concentrations overcomes the need to calculate glucose t1/2 values. The high glucose concentration at 0 minutes found in this study may reflect a more realistic concentration to use in assessing client-owned cats in a hospital environment.