['Lispro is a newly FDA-approved analog of human insulin that will be widely used in patients with IDDM. This insulin, however, may have an increased potential for hypoglycemia because of its very rapid subcutaneous absorption, especially in a setting of decreased carbohydrate intake. Using a short-term prospective randomized parallel group-study design, we studied the incidence of hypoglycemia when lispro was given before breakfast compared with regular human insulin. Since carbohydrate intake is a determinant of postprandial glycemia, we administered three isocaloric meals characterized by low, average, and high carbohydrate content.', 'Two groups of six IDDM subjects were randomized to receive 0.15 U/kg of lispro or regular human insulin subcutaneously before the ingestion of three 500-kcal breakfast meals of differing carbohydrate content on separate days. Lispro was administered at mealtime, and regular insulin was administered 30 min before mealtime.', 'Postprandial plasma glucose concentrations were decreased in the lispro group compared with the regular-insulin group for all three meal types (P < 0.05), and hypoglycemia developed more frequently and rapidly in the lispro group, compared with the regular-insulin group by survival analysis. Additionally, peak insulin concentrations were higher (P < 0.001) and peaked more rapidly (P < 0.05) in the lispro group, compared with the regular-insulin group.'] Is meal composition a determinant of lispro-induced hypoglycemia in IDDM?