Twofold differences in gene expression levels can be vital for an organism. This is beautifully illustrated by the process of `dosage compensation' in Drosophila, which doubles transcription from the single male X chromosome to equal the mRNA levels originating from the two X chromosomes in female cells. Failure of the process leads to male-specific lethality. A number of recent publications have furthered our understanding of the ribonucleoprotein complex, which mediates dosage compensation and how it targets the male X chromosome. Deciphering the principles of X chromosome recognition and the nature of the chromatin configuration, that allows fine-tuning of transcription, remain the most interesting challenges.