Polycomb group proteins are chromatin regulators with highly conserved functions. The Polycomb repressive complex 2 (PRC2) methylates H3K27 to stably silence target genes, including the HOX genes in Drosophila. More recently, Utx and Jmjd3 demethylases were found to reverse PRC2-mediated H3K27 methylation, and it has been suggested that a dynamic cycle of methylation and demethylation is required for appropriate regulation of gene expression. Now, Ömer Copur and Jürg Müller challenge this view (p. 3478), via the analysis of Drosophila Utx mutants. Lack of zygotic Utx function has no effect on Drosophila development, although mutant adults die shortly after hatching. Loss of both maternal and zygotic Utx, however, leads to larval death and to defects in HOX gene expression - in both the embryo and larval imaginal discs. Thus, it appears that Utx in Drosophila - and, by inference, H3K27 demethylation - is required only at early stages to set up the patterns of HOX expression; it is largely dispensable later in development, suggesting that H3K27 methylation may in fact be very stable.