Trypanosomes and other protozoa, such as Chlamydomonas, move using flagella powered by dynein motors. These contain one or more catalytic heavy chains and several light and intermediate chains, but how these subunits contribute to motor assembly and function is poorly understood. Kent Hill and colleagues now report that the T. brucei dynein light chain 1 (TbLC1) stabilises the outer dynein arms and is required for forward flagellar motility (see p. 1513). The authors show that TbLC1 is localised along the length of the flagellum and that knocking it down by RNAi causes complete loss of the normal tip-to-base flagellar beat and the emergence of a reverse beat that moves the cells backwards. They also report that the outer arm dyneins are disrupted in TbLC1 mutants, a surprising result given that Chlamydomonas LC1 binds to the catalytic domain of dynein rather than to the domain involved in its oligomerisation. Overall, this first analysis of LC1 function provides important insights into flagellar motility that could aid efforts to exploit the trypanosome flagellum as a drug target in sleeping sickness.