Type 2 diabetes mellitus is a metabolic disorder that results from defects in both insulin secretion and insulin action. Questions remain about when insulin therapy is indicated; thus, the aim of this study was to evaluate homeostasis model assessment beta-cell (HOMAbetacell) values as surrogate criteria for insulin therapy indication in patients with type 2 diabetes. A prospective study was performed involving 189 type 2 diabetic patients with deficient metabolic control assessed by clinical and laboratory parameters. All patients received nutritional intervention and combination therapy with metformin and glimepiride. Patients who did not respond were admitted to the next phase, which consisted of glimepiride + metformin + rosiglitazone oral therapy and revaluation after 3 months. Comparisons between responders and nonresponders in this phase were made in order to achieve differences in metabolic parameters and beta cell function. Of 189 patients studied, 150 (79.36%) were considered full responders in the first phase of this study. The remaining 39 patients were admitted in the second trial phase, in which 20 patients (51.28%) responded to triple oral therapy, while the other 19 (49.72%) required insulin therapy. Significant differences were found in fasting and postprandial glycemia (P < 0.001; P < 0.004) between the non-insulin-requiring group (200 +/- 12.0 mg/dL; 266.05 +/- 17,67 mg/dL) and the insulin-requiring group (291.5 +/- 17.6 mg/dL; 361.6 +/- 26.1 mg/dL). Likewise, significant differences were observed in homeostasis model assessment insulin resistance (HOMAIR) and HOMAbetacell values (P < 0.002; P < 0.04) between non-insulin-requiring patients (7.7 +/- 0.8; 24.5 +/- 1.3%) and insulin-requiring patients (12.6 +/- 1.2; 19.4 +/- 2.4%). Finally, significant differences were observed when comparing body mass index (non-insulin-requiring group, 29.2 +/- 0.4 kg/m, versus insulin-requiring group, 27.1 +/- 0.9 kg/m; P < 0.05). HOMAbetacell determination in clinical practice is a useful tool to determine when insulin therapy should be started for type 2 diabetic patients.