The lengths of rhythmical units (as defined by Karl Marbe in 1904) were identified, and their frequencies counted, in twelve complete texts from the Aix-MARSEC database of formal spoken British English. The texts all belonged to the genre of current affairs com¬mentary. L-motifs (i.e. maximal monotone non-decreasing sequences) of the rhythmical unit lengths were also identified, and the frequencies of the different L-motif lengths were count¬ed. The frequencies of both rhythmical unit lengths and L-motif lengths were modelled using a continuous approach with the Zipf-Alekseev function. Good qualities of fit were obtained for both kinds of unit on all texts. The parameters a and b of the Zipf-Alekseev function for the rhythmical unit lengths (though not for the L-motif lengths) were also found to be related in the form of a further Zipf-Alekseev function. Further research should aim to extend the application of the motif approach to rhythmical units.