Hansenula polymorpha Pex14p is a novel peroxisomal membrane protein essential for peroxisome biogenesis. In vivo labeling experiment of wild-type cells with 32P-orthophosphate and alkaline phosphatase treatment of labeled Pex14p indicate that Pex14p is phosphorylated in vivo. Analysis of the phosphoamino acid in the phosphorylated Pex14p suggested that the major phosphoamino acid was acid labile. Using expression system of several truncated Pex14ps in a PEX14-deletion strain it is suggested that the phosphorylation site of Pex14p resides in the C-terminal 58 residues.