Preliminary quantitative studies using 10% and 20% dietary protein levels were made on the relationship between heterozygous albino female mice and Nematospiroides dubius (Nematoda: Heligmo-somidae) under conditions of initial challenge of the host by the nematode. N. dubius produced effects on the hosts'' growth curve and blood cellular elements. The 20% protein diet protected mice against these effects, while the 10% diet permitted more severe and more prolonged disturbances.