The periodic pattern of the supraorbital lateral line organs forms in the epidermis of Xenopus by the subdivision of a streak-like primordium into a linear series of small cell groups. In normal development, each such organ initially contains about 8 cells (Winklbauer & Hausen, 1983a,b). To see whether this initial organ size depends on the size of the streak-like primordium at the time of organ segregation, primordium size was reduced experimentally before the onset of pattern formation. In such small primordia, the size of the primary organs formed is not adjusted so as to allow the formation of a normal number of organs. Instead, the initial organ size is kept approximately normal, and the number of organs is correspondingly reduced, i.e. the pattern forming mechanism is not capable of 'size regulation'.