Partially dolomitized, nodular and mottled limestones comprise most of the Middle Devonian (Eifelian) Elm Point Formation in the Paleozoic outcrop belt of southern Manitoba. Fabric-selective dolomite occurs in all of these platform limestones and consists of: (1) microdolomite inclusions in echinoderm grains; (2) microcrystalline dolomite in micritic components; and (3) fine- to medium-crystalline dolomite in micritic components. The first two dolomite types are considered to be byproducts of the stabilization of high Mg calcite precursors. The third dolomite type is interpreted to be of early diagenetic origin and formed from Middle Devonian seawater. The findings also tentatively suggest that there is no genetic linkage between dolomites of the Elm Point and overlying Winnipegosis Formations, implying that the Elm Point was not a conduit for dolomitizing fluids flowing upward into Winnipegosis carbonate buildups. The fabric-selective nature of Elm Point dolomites suggests that the nature of the host rock, i.e., intrinsic factors, played a major role in determining the extent of dolomitization. Formation of dolomite Type 3 occurred only in permeable and porous sediment which locally had been modified by burrowing, boring and microbial micritization. Early lithification of lime mud, indicated by intraclasts and hardgrounds, locally reduced permeability and porosity, inhibiting dolomitization.