In Ontario, the secondary school science curriculum advocates the use of laboratory activities to reinforce specific scientific concepts and promotes the development of skills in scientific investigation and communication. Students in biology courses are often expected to identify unknown substances using standard tests, but rarely are these tests integrated into a problem-based learning situation. This activity provides an opportunity for students to demonstrate critical thinking and deductive reasoning skills, while also demonstrating procedural aptitude. To be successful, students must conduct a series of controlled experiments and, by analyzing the results, solve the dilemma of which food to serve to which hospital patient.