This Missa Brevis Rhythmica is dedicated to Rødovre Statsskoles Choir and Orchestra, Copenhagen, and is composed for a concert in Hamburg February 28th 1977. In the foliowing lines you will find some practical advice on how to perform the Missa Brevis Rhythmica. In the Kyrie movement there is a rather long passage (bar 57 - 88), and the idea is that the two soloists might improvise here. This passage can be shortened or lengthened according to the wishes and abilities of the soloists. The idea of improvisation as such is a very important one in the work and this goes for the soloists as well as for the piano', electric-bass, and the rhythm, as can be seen from the use of the indicated harmonies. As for the piano the required accompaniment has been written down in certain cases, in other cases, only the harmonies indicated. In accordance with the idea of improvisation other groups of instruments can be added, such as maraccas, drums, organ, string-moog, etc. Where improvisation is possible and desirable it is indicated in the music by means of a sign (improvisation) and here a good result is of course dependent on good musicians. The duration of the work is approximately 20 minutes.