Although good material is scarce, 109 small fluid inclusions in sphalerite were studied, at least some of which are probably primary in origin. Most samples came from mines or drill cores in the Viburnum Trend in southeast Missouri.Metastability was observed frequently during freezing point determinations. Freezing temperatures are mainly in the range --20 to -- 28 degrees C, corresponding to very saline brines; homogenization temperatures are mainly in the range 94 degrees to 120 degrees C. These sphalerite fluid inclusion data fit into the ranges observed for the ore-depositing fluids in most Mississippi Valley-type deposits, even though the district is different in some respects.In addition, primary inclusions were studied from the associated, but presumably later, gangue calcite. Fourteen inclusions in Viburnum calcite all contain brines which are much less saline. Most inclusions out of 16 in calcite from three areas in the nearby Old Lead Belt yielded similar low salinities. Twelve inclusions in sphalerite from pyrite-sphalerite-calcite veins in the Precambrian basement beneath the Fletcher mine have trapped hotter, more dilute fluids and hence represent a different mineralization.