The occurrence of ionospheric irregularities was studied using Global Positioning System (GPS) measurements at Tucumán (26.9° S, 294.6° E; geomag. lat.: −15.5), a station placed near the souther peak of the equatorial anomaly. Radio scintillations at the GPS L1 frequency (1.575 GHz) were monitored using the GPS receiver installed at the mentioned station. The considered measurements were obtained during September 1998 – April 1999 period. The results show that amplitude scintillations frequently occur between 21 and 02 LT. Scintillations are more frequent when the satellites are in the northwest — northeast sector of Tucumán's sky. Strong scintillations were observed in about 40% of the nights.