A single blind dose response study of the effects of treatment with tablets containing 50-400 micrograms of desmopressin was conducted in 15 children with primary nocturnal enuresis. A dose response effect was seen, with the 100, 200, and 400 micrograms doses resulting in significantly more dry nights than when a placebo was used. The response after 200 micrograms was significantly different from that after 100 micrograms (p less than 0.02) but not from that after 400 micrograms. A randomised, double blind, double dummy, cross over study was then carried out in 30 children to compare the effects of a 20 micrograms dose given through a nasal pipette, a 200 micrograms tablet, and a placebo. The numbers of dry nights were significantly greater during both periods of treatment with desmopressin when compared with that using placebo, but there were no differences between the methods of taking the drug. After oral and nasal treatment 41% and 52%, respectively, of the patients improved by more than 50%. Nine children (31%) remained completely dry after treatment.