To compare the efficacy of different doses of fentanil, remifentanil, and alfentanil co-administered with propofol in patients undergoing minor surgery. Materials and methods: This double-blind, multi-centered, placebo-controlled study was conducted in 2 medical centers. One hundred forty-one ASA class I and II adult patients aged 18-65 years were included in the study. Patients received i.v. 1 µg kg-1 fentanil (group F, n = 33), 10 µg kg-1 alfentanil (group A, n = 33), 0.5 µg kg-1 remifentanil (group R, n = 36), or saline (control group, n = 39) co-administered with propofol 2.5 mg kg-1 without additives over 30 s. An LMA was inserted 90 s later. Conditions for the LMA insertion were assessed. The number of attempts, airway quality, and hemodynamic changes were recorded. Results: There were no significant differences in the demographic data among the groups. The LMA was more easily placed in the remifentanil group compared with the other groups . All first attempts for the LMA insertion were successful in the remifentanil group. When the opiates groups were compared with the control group, easier insertion rates were detected in all the opiate groups. LMA insertion was easiest in the remifentanil group, followed by the alfentanil, fentanil, and control groups, in that order. Heart rates and blood pressures were reduced in all groups, but no treatment was required. Conclusion: Opiates co-administered with propofol improved the LMA insertion conditions compared to propofol alone. Out of the opiates, remifentanil had the highest success rate.