Ionospheric electron content was monitored from sites in or near Tromsø, Norway, for six months of 1993, using the transmissions from the satellites of the Global Positioning System (GPS). The data have been used for preliminary studies of two important phenomena of the high-latitude ionosphere: the main trough and the incidence of large irregularities. The latitude and motion of the trough were determined on several occasions during the spring period, and the results compared with previous data. Best agreement is with the formula of Collis and Haggstrom (1988). The incidence of large irregularities was surveyed during a four-month period, approximately from the summer solstice to the autumnal equinox, and the variation with time of day and magnetic activity has been determined. It was found that irregularities are considerably larger by night than by day, but that they are enhanced during both periods by increased magnetic activity. Statistical results are presented. It is suggested that these irregularities are the same as the “auroral blobs” previously studied by incoherent-scatter radar.