Knockouts by homologous recombination are frequently used to investigate the function of genes in Dictyostelium and other organisms. Antisense-mediated gene silencing and RNA interference (RNAi) are convenient alternatives to reduce gene expression to different levels and to silence multigene families. We describe here the methods for efficient RNA interference in Dictyostelium and some useful mutant strains that enhance the success rate or may serve as convenient controls. We believe that it is helpful to also discuss failed attempts to optimize and expand the system because these are rarely discussed in the literature. In addition, a list of in silico and experimentally identified components in the RNAi and antisense pathway is presented.