Fluctuations in concentration of the starting materials during continuous diazotization are taken into account by passing a component stream from the receiver to the diazotization vessel through an analyser where, for a short residence time, the nitrite content is determined by an electrochemical measuring technique. A required nitrite excess is adjusted in the receiver on the basis of this measurement. By virtue of the pH-value, however, a diazotization reaction still does not take place in the receiver.