Abstract Against the background of the synergetic approach to language some hypotheses about the relation between word length and morpheme length are discussed. First of all, Menzerath's law on the word‐morpheme level is given. On the basis of this law, a function is derived which reflects the dependence of the number of graphemes of a word on its number of morphemes. Furthermore, the influence of morpheme length on the number of graphemes of words containing morphemes of this length is analysed. It is shown that this relation is not just proportional. The results of statistical tests which were realised with the help of the CELEX lexical database are given. They show that all of these hypotheses can for the present be accepted as valid for the languages English, German and Dutch.