First choose one of the given keys for amoebae and flagellates, for plasmodia, for helminth ova or for microfilariae. You are provided with images of parasites in a random order and the first question of a decision tree with a series of answers. On “mouse-over” you are given pencil drawings showing the diagnostic features. You choose the answer and you get the next question and so on. At the end of the decision tree, you are given the image of the parasite you identified and the answer whether this is right or wrong. You can display the right diagnostic path by clicking (right answers in green) and you can see where you made a mistake (wrong answer is in red). With the “again key” you can restart the decision tree; with the “next key” you get a new diagnostic task.