This study examines the influence of urban and meteorological factors on the surface air temperature field of the medium-sized city of Szeged, Hungary, using mobile and stationary measurements under different weather conditions between March and August 1999. This city, with a population of about 160 000, is situated on a low, flat flood plain. Efforts have been concentrated on investigating the maximum development of the urban heat island (UHI). Tasks include the determination of the spatial distribution of seasonal mean maximum UHI intensity and modelling of existing conditions in the period being studied. Multiple correlation and regression analyses are used to examine the effects of urban parameters (land-use characteristics and distance from the city centre determined in a grid network) and of meteorological parameters (wind speed, temperature) on thermal conditions in the study area. The results indicate isotherms increasing in regular concentric shapes from the suburbs towards the inner urban areas where the mean maximum UHI intensity reaches more than 3 °C in the studied periods. A strong relationship exists between urban thermal excess and distance, as well as built-up ratio. In contrast, meteorological conditions do not have any significant effect on the UHI intensity at the time of its maximum development.