Recently, we have identified a cDNA encoding a novel protein Ser/Thr phosphatase (EC 3.1.3.16) from Arabidopsis thaliana (L.) Heynh. (ecotype Columbia), designated as PP7, which is only distantly related to the known phosphatases of the PPP family. We examined PP7 expression in A. thaliana using Northern blot analysis, reverse transcriptase-polymerase chain reaction (RT-PCR) and whole-mount in situ hybridisation. Although the PP7 transcript could be detected in all organs analysed by the first two methods, whole-mount in situ hybridisation revealed specific expression in a subset of stomata in A. thaliana seedlings. Possible implications of this expression pattern are discussed.