Methylglyoxal in New Zealand manuka honey has been shown to originate from dihydroxyacetone, which is present in the nectar of manuka flowers in varying amounts. Manuka honey, which was freshly produced by bees, contained low levels of methylglyoxal and high levels of dihydroxyacetone. Storage of these honeys at 37 degrees C led to a decrease in the dihydroxyacetone content and a related increase in methylglyoxal. Addition of dihydroxyacetone to clover honey followed by incubation resulted in methylglyoxal levels similar to those found in manuka honey. Nectar washed from manuka flowers contained high levels of dihydroxyacetone and no detectable methylglyoxal.