Treacher Collins syndrome (TCS) is an autosomal dominant craniofacial disorder involving the mid and lower face and, in particular, the tissues affected arise solely from embryonic branchial arches I and II. TCOF1, the gene involved in TCS, has been cloned and although the function of the encoded protein, treacle, has not yet been established, it exhibits peak expression in the branchial arches. Treacle contains a series of repeating units of acidic and basic residues, which are predicted to contain putative casein kinase II (CKII) and protein kinase C (PKC) phosphorylation site motifs. In addition, treacle has weak homology to two phosphorylation-dependent nucleolar proteins, which shuttle between the cytoplasm and nucleolus. Based on these observations, phosphorylation of treacle may be important for its function. In this study, GST-treacle fusion peptides were constructed using particular TCOF1 exons that contained potential CKII and PKC phosphorylation sites. These were used as substrates in in vitro kinase assays and showed that treacle fusion peptides can be phosphorylated by the appropriate kinases. Furthermore, using tissue extracts we have demonstrated that in avian embryonic branchial arches I and II there is a kinase activity that can phosphorylate treacle peptides that is consistent with CKII site recognition. This activity coincides with the reported high expression of treacle in these tissues at early developmental stages and declines later in development.