An analysis has been carried of the correlation of the occurrence of type III bursts and flares in spotless regions over the past ten years. As a comparison, the same study has been performed also for flares covering major sunspot umbrae (i.e. in magnetic conditions presumably opposite to the above). The results show a very low correlation of the former flares with type III bursts (8%) and a higher than average value for the latter flares (36% against the normally accepted 25%). Thus an important role of the ambient magnetic field on the generation of type III events seems well established. The effect of the presence of surges and of rapid brightness rises (‘flash-phases’) on the correlation with these bursts has been examined: both features appear to improve the correlation. Some considerations regarding the results of other researches as compared to this one are outlined.