Male patients displaying an immotile or almost immotile sperm population are the object of an interdisciplinary study concerning a ciliary mutant that induces the "Immotile-Cilia Syndrome". Development and function of both sperm flagella and cilia are normally affected because of disturbances of the 9 + 2-arrangement. During this program, clinical, physiological, genetical and ultrastructural investigations were done. The ultrastructure of immotile spermatozoa of an infertile man did not reveal inner and outer dynein arms. Lack of the ATPase dynein which is essential for movement of the 9 + 2-axoneme, is typical for the above syndrome. In addition, symmetry of the fibrous sheath of the spermatozoa was very abnormal. The pneumologist examined normal lung function, where the ultrastructure of the cilia of the nasal mucosa displayed the dynein arms. Analysis of family tree and chromosomes by the geneticist also gave a normal result. As revealed by this infertile patient it seems likely that expression of dynein must not be identical in both germ cells and somatic cells. Such variations are therefore regarded as additional forms of the "Immotile-Cilia syndrome". Asymmetric fibrous sheaths are thought to be a result of immotile spermatid flagella, leading to an abnormal arrangement of the accessory axonemal structures. Normal early spermatid flagella of man and rat show specific movements.