Methods for constructing engineered "tissues" from simple suspensions of cells are valuable for investigations into basic developmental biology and for tissue engineering. We recently published a method for producing embryonic renal tissues from suspensions of embryonic mouse renal cells. This method reproduced the anatomies and differentiation states of nephrons and stroma very well; it had the limitation, however, that what would, in normal development, be a single, highly branched collecting duct tree leading to a ureter developed, in the engineered system, as a multitude of very small collecting duct trees. These were isolated from each other and therefore would not be effective for draining urine to a common exit, were the tissue to be supplied with blood and physiologically active. Here, we report an improvement on the original method; it results in the formation of nephrons arranged around one single collecting duct tree as would happen in a normal kidney.