The floral homeotic geneAGAMOUS (AG) imparts carpel identity on the fourth whorl of floral organs in wild-typeArabidopsisflowers. Less is known about the genes that regulate carpel patterning and differentiation. To identify candidate regulators, we screened for genes expressed in developing carpels. SinceArabidopsiscarpels are difficult to isolate, we used whole inflorescence apices of two floral homeotic mutants (pi and pi ag) and mRNA differential display, to identify carpel transcripts. Two of the resulting cDNA clones were shown to be expressed predominantly in flowers. They encodedAGL11,a MADS box transcription factor known to be expressed in the carpel and ovules, and a novelArabidopsisendo-1,4-β-D-glucanase (ATCEL2).In situhybridisation localised theATCEL2transcript to the developing septum and ovule primordia of young carpels.