Practical laboratory work in parasitology can be very limited, due to the difficulty in maintaining multi-host parasite life cycles, especially for a large, once-yearly undergraduate laboratory class for life science students. The use of mackerel, "Scomber scombrus," bought from a local fishmonger, is an ideal model to investigate important parameters of infection with the nematode worm, "Anisakis simplex." This simple experiment, involving nothing more than measurements, dissection and observation, yields reliable data to demonstrate the principles of the intensity, prevalence and overdispersion of infection, and allows statistical analysis of any variation in these parameters in relation to the weight and sex of the fish host. (Contains 2 tables and 5 figures.)