Over the past decade, immunotherapy has emerged as a promising alternative form of cancer treatment with the potential to eradicate tumour metastasis. Unfortunately, its curative potential is in general limited by immunosuppressive proteins that negatively regulate dendritic (DC) and/or T-cell function. The recent discovery of RNA interference (RNAi) has facilitated the study of gene function in immune cells and recent data indicate that DC maturation, function, and survival can be modulated by small interfering RNAs (siRNAs) targeting genes involved in immune suppression. This chapter describes detailed protocols for introducing siRNAs into human monocytes and dendritic cells using standard electroporation techniques.