Because our group was in Chicago and then Madison, far from the sea, our attention was often directed to foods other than shellfish. We considered that foods might be liquids, or solids that could be contaminated in depth, or solids with superficial contamination limited to a relatively impermeable surface. The most challenging of these would be solids that could be contaminated in depth-our first model system comprised cottage cheese and CA9 (Herrmann and Cliver 1968a). An inoculated, 25-g sample was slurried with 100 ml glycine-NaOH buffer, treated with Freon TF (1,1,2-trichloro-1,2,2,-trifluoroethane) and bentonite, clarified by centrifugation, and concentrated by a two-stage (PEG dialysis followed by ultracentrifugation) process that yielded 0.5 ml for testing in cell culture. Virus recoveries from the samples inoculated with 50 PFU or less were roughly 50%, as determined by the plaque technique. In addition to cottage cheese, the method was then adapted and tested with beef with gravy, carrots, chicken pot pie, chocolate éclairs, clams, ground beef, peanut-butter sandwiches, potato salad, and strawberries. The beef with gravy and the peanut-butter sandwiches had been freeze-dried to be fed to astronauts early in the US space program (Herrmann and Cliver 1968b). Viruses inoculated included CA9, coxsackievirus B3 (CB3), and EC6; poliovirus 2 was used in experiments on recovery of antibody-neutralized virus. Not surprisingly, optimal extraction methods varied among foods, with bentonite omitted and serum substituted for low-protein foods. Recoveries of EC6 were somewhat less than those for the coxsackieviruses. Overall, it was found that a 25-g food sample must contain at least 3-4 PFU for a 50% probability of detecting virus. We supposed that viral contamination of tomatoes would be largely limited to the surface, so we devised an apparatus that would dislodge virus from the tomato surface without suspending the food solids in the extract . Surface dirt, fecal solids from the model contaminant, and a variety of bacteria appeared in the washings and had to be dealt with before the concentration step; recoveries of CB3 were roughly 49%, with a 50% endpoint, for a positive test result, of slightly under 2 PFU per tomato.