We discuss the results of experiments carried out with a z pinch of plane configuration and a theta pinch of round cross section. It is shown that under certain discharge conditions the behaviour of the plasma in these pinches is characterized by a far-reaching analogy. On this basis an attempt has been made to use the results of investigation of the plane z pinch for a better understanding of the processes under the complicated conditions of discharge in a theta pinch with a trapped reverse field. In particular we consider a possible mechanism of plasma rotation that has been observed in the theta pinch.under these discharge conditions.