This review concerns the general problem of understanding growth control in the whole organism, starting with a saltatory change in size generated by a chromosome translocation or a mutation in a single gene. In particular, changes in insulin-like growth factor-II levels, by genetic and embryological manipulation, have major effects on wet weight size, but the intermediary events that link these levels to this measure of growth are uncertain. Thus it is currently impossible to eliminate any of the intermediary candidate processes that have been observed in model systems, including changed rates of apoptosis, cell multiplication, protein synthesis, capillary permeability and fluid transport.