Background/Aim: Despite combined therapy consisting of surgery, external X-ray, and medical therapy, a significant number of acromegaly patients continue to have uncontrolled growth hormone (GH) secretion and active disease. These patients, particularly those with large or invasive tumors, require additional therapy to decrease their GH levels. Our aim was to investigate whether patients with documented GH-secreting pituitary adenomas leading to acromegaly would respond with attenuation of GH and insulin-like growth factor-1 (IGF-1) levels after treatment with a peroxisome proliferator-activated receptor gamma (PPAR-γ) agonist. Methods: We conducted prospective analyses in the Endocrinology Clinic of the Pamukkale University. Acromegaly patients who had active disease participated in two admissions: before and after 6 weeks of daily treatment with 8 mg of oral rosiglitazone. Four male and 3 female patients have completed the study. Basal and nadir GH levels during an oral glucose tolerance test were determined, and the IGF-1 and IGF-binding protein-3 levels were also measured both before and 6 weeks after the rosiglitazone treatment. Results: Treatment with rosigitazone did not reduce basal and nadir GH levels during the oral glucose tolerance test and the IGF-1 levels in the patient population as a whole (p > 0.05). Conclusions: The PPAR-γ activator rosiglitazone, used at maximum approved dosage, did not reduce plasma GH and IGF-1 levels in patients with acromegaly. Further studies with higher doses and longer duration of PPAR-γ agonist administration would be required to determine its usefulness in the treatment in this group of patients.