The study addressed a previously neglected issue in the concept of working memory, namely whether or not rhythmical information is coded and maintained in a phonological loop. Thirty subjects engaged in a task which required them to reproduce the temporal sequence of rhythm. The results showed that the reproduction of rhythm was dramatically reduced by a concurrent articulation, and that the deterioration of rhythm reproduction was larger than that obtained with a concurrent spatial task which would not diminish the activity of the phonological loop directly. An articulatory component of the working memory apparently plays an important role in memorizing rhythms. Furthermore, the sparse-dense rhythm (a pattern which started with sparse temporal structure and ended with a dense one) allowed better memorization than a dense-sparse pattern. The sources of the sparse-dense superiority effect are discussed in terms of the working memory for rhythmic information.