5 years ago we decided to try to work out how the parasite load we see in human malaria patients is determined by parasite multiplication rate, parasite growth inhibition by the host response, and duration of infection. The big problem was that in humans with naturally acquired malaria we cannot measure any of these directly. Our attempts to solve the problem took us back in time to data generated almost 100 years ago, then forwards to discover novel mechanisms of host defense against malaria.