Fluid inclusions in halite are widely used in research to determine the conditions of sedimentation in salt basins and reconstruct the chemical composition of seawater during a specific geological period. However, previous preliminary studies of the genetic types of inclusions, considered in the present research project, have not received due attention. Consequently, we decided to take into account the main distinguishing features of fluid inclusions in halite, belonging to various genetic types. The ultramicrochemical analysis (UMCA) method is one of the several methods that are used for the quantitative determination of the chemical composition of the primary fluid inclusions in halite. We have upgraded that technique, and that allowed us to reduce the analytical error rates of each component determination. The error rates were calculated in the study of Ca-rich and SO4-rich types of natural sedimentary brines.