This book is one of the single most complete pieces on gastrointestinal (GI) nematode infections. The review chapter is quite intensive. The steps in developing a laboratory model for the preliminary study of GI nematode infections in small ruminants in particular and other domestic animals in general are outlined through various experiments that were performed. Some of the factors which are known to influence the responses of host animals particularly small ruminants to their GI nematode parasites were examined in outbred albino mice. The idea was that if mice responded to its natural trichostrongylid parasite, Heligmosomoides bakeri in exactly the same way as the ruminants do to their own natural parasites especially Haemonchus contortus which is also a trichostrongylid and a blood sucker like H. bakeri of mice, then the H. bakeri-mouse model can be a suitable model for the preliminary study of some aspects of GI nematode infections of small ruminants and other ruminants or livestock in general. The results largely showed similarities in the way the outbred albino mouse and ruminants responded to their various GI nematodes.