Аннотация:Common star complexes are huge (0.3–1 kpc in diameter) groups of relatively young
stars, associations and clusters. The complexes usually form regular chains along spiral
arms of grand design galaxies, being evidently formed and supported by magneto-
gravitational instability developing along an arm. Special attention is given to a few
large complexes which have signatures of gravitational boundness, such as round shape
and high central density. Concentrations of stars and clusters in such a complex in M51
galaxy were found in this paper; we concluded it is possible to suggest that the complex
is gravitationally bound. It is also stressed that some properties of the giant complex
in NGC 6946 (such as its semicircular and sharp Western edge) are still enigmatic.