The aim of the study was to assess the effects of the combination of metformin plus pioglitazone or rosiglitazone on glucose and blood pressure in type 2 diabetic patients with metabolic syndrome, as well as its tolerability in those patients. In this 12-month, multicentric, double-blind, randomized, controlled, parallel-group trial, all patients began with metformin. Patients were randomized for self-administration of either pioglitazone or rosiglitazone for 12 months. We assessed body mass index (BMI), glycemic control (glycosylated hemoglobin [HbA(1c)], fasting and postprandial plasma glucose and insulin levels [FPG, PPG, FPI and PPI, respectively] and homeostasis model assessment [HOMA] index) and systolic and diastolic blood pressure (SBP and DBP, respectively), at baseline and at 3, 6, 9 and 12 months of treatment, as well as high-sensitivity C-reactive protein (hs-CRP), nitrites/nitrates and adiponectin (ADN) at baseline and at 12 months of treatment. Significant HbA(1c) decreases were obtained after 9 (p<0.05) and 12 (p<0.01) months in both groups. After 9 and 12 months, mean FPG and PPG levels were decreased in both groups (p<0.05 and p<0.01, respectively). We observed decreases in FPI and PPI at 9 and 12 months (p<0.05 and p<0.01, respectively) compared to the baseline values in both groups. Furthermore, HOMA index improvement over the baseline value was obtained only at 12 months (p<0.05) in both groups. SBP and DBP improved significantly (p<0.05, for each) in both groups after 12 months. hs-CRP decreased significantly (p<0.05) in both groups after 12 months; nitrites/nitrates and ADN increased significantly (p<0.05, for each) in both groups after 12 months. The combination of thiazolinediones and metformin is associated with a slight but significant improvement in the long-term blood pressure control of these patients, and with an improvement in the anti-inflammatory state, both of which are related to a similar reduction in insulin-resistance.