The parasitic nematode Ascaris lives in the low-oxygen intestinal folds of over one billion people world-wide. The worm has an octameric hemoglobin that binds oxygen four orders of magnitude more tightly than does human hemoglobin. Our studies have focused on elucidating the molecular mechanism of oxygen avidity, the basis of multimerization and the function of this remarkable molecule. We now believe that we understand a fair amount about the molecular interactions that result in enhanced avidity, have some preliminary ideas on octamer formation, and have some hypotheses about possible function. Along the way we have stumbled into the disciplines of intron evolution, sterol biosynthesis and oxygen-regulated gene expression.