Whereas the song of the great reed warbler has been studied in different aspects no attention has been paid to its organization up to now. Here we represent some results of studies on songs of individually known birds in a colour-ringed population at Lake Muggelsee in Berlin, Germany. The length of 506 songs varied between 1.3 and 14.7 s. The means of song length of 12 birds varied between 3.36 and 5.87 s. They are not influenced by date of recording or repertoire size but depend on the number of syllables per song. Song length and length of song intervals (1.2 to 23.5 s) are not correlated, with the exception of three birds. There was no important difference between the repertoire sizes of ten analysed males. They varied between 42 and 57 syllables and were independent of mating status (polygynous vs. monogamous), which is in contrast to the results of Catchpole (Behav. Ecol. Sociobiol., 19, 439-445). The total number of syllable types of ten birds recorded in 1993 was 71, of which 19 were represented in all birds and 14 in 9 birds. Cumulative plots of new syllable types produced in consecutive songs indicate that there is only a small increase of new syllable types after the 35th song. There was no increase of new syllables after song-post change, in contrast to what was shown by Luschi for male Sardinian warblers (Bioacoustics, 4, 235-244). The song is an alternation of high-pitched and noisy phrases. The phrases consist of 1 to 10 syllables. Although there are some typical intruding elements of songs no general pattern of organization could be found. The same song does not appear twice in one song bout in the same order of phrases and with the identical number of syllables. The syngraph of syllables is interfluent. The degree of organization seems to become higher during the breeding season. The relationships between preceding and following syllables are similar to those of the sedge warbler found be Catchpole (Behaviour, 29, 226-246), probably showing a Markovian chain of the first order. Alternations of homologous syllables are dominant, but some heterologous alternations were found more often than expected by chance. These similarities in song structure in both Acrocephalus species indicate the same principles of song organization in the genus.