Considering coliphage T4 as the pathogen and its host bacterium as the organism susceptible to infection, this kit enables students to study the action of antibody on a disease agent. The neutralization of phage T4 infectivity by homologous antibody is demonstrated through plaque assays in host E. coli B and the kinetics of antibody action are examined. Materials include coliphage T4 and antiserum, a fresh agar slant culture of host bacteria, agar base layer media and soft agars for bioassays, tubes of sterile broth for cultures and dilution series, 1-mL pipets, and instructions written for 1 to 5 students. Kit contains coupon for prepaid delivery of perishable materials. Return coupon at least 2 weeks prior to requested delivery date to ensure prompt arrival of materials.