As assessed by RNA blot analyses with gene-specific probes, we report that the perivascular connective tissue mast cells (CTMCs) in the ear and skin of BALB/cJ mice contain abundant levels of the mouse mast cell protease (mMCP) 7 transcript, in addition to those protease transcripts present in their serosal mast cells (SMCs). High levels of the mMCP-7 transcript also were detected in the ears of WBB6F1/J(-)+/+, WCB6F1/J(-)+/+, WB/ReJ(-)+/+, and WC/ReJ(-)+/+ mice. However, the ears of these four strains and the SMCs from the WCB6F1/J(-)+/+ strain but not the BALB/cJ strain also contained high steady-state levels of the mMCP-2 transcript. The mMCP-2, mMCP-4, mMCP-5, mMCP-6, and mMCP-7 transcripts were not detected in the ears of mast-cell-deficient WBB6F1/J-W/Wv and WCB6F1/J-Sl/Sld mice, indicating that mast cells were the source of these protease transcripts in the +/+ animals. When immunohistochemical analyses of serial sections of ear and skin from WBB6F1/J(-)+/+ mice were performed with anti-mMCP-2 IgG and anti-mMCP-5 IgG, the perivascular CTMCs in these tissues were found to express both mMCP-2 and mMCP-5 in their granules. The prominent expression of mMCP-7 in constitutive perivascular CTMCs indicates that this mast cell has an extended protease phenotype relative to the SMCs of the same strains. Further, the perivascular CTMCs and SMCs of the +/+ strains differ from those in BALB/cJ mice in their prominent expression of mMCP-2.