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A procedure is described for designing open-tubular liquid chromatographic (LC) columns with high resolving power, optimized for mass loadability. Large film thicknesses improve the loadability, but decrease the efficiency owing to the increased mass-transfer term. Normally an arbitrary upper limit of the magnitude of the contribution of the stationary phase mass-transfer term to the overall plate-height equation of about 20% is accepted. The present approach allows the real optimum value of the contribution of the stationary phase mass-transfer term to be calculated. The optimum was found to occur at about 50% in most instance. This corresponds to a plate height equation h = 2/ v + 0.12 v for k ′ = 3 instead of the expression for very thin films h = 2/ v + 0.08 v as advocated by Knox and Gilbert ( h = reduced plate height, v = reduced velocity; k ′ = capacity factor). The maximum column length is about 5 m for all phase systems with 3 · 10 5 theoretical plates, dead time of mobile phase 1000 s and 20 MPa pressure drop along the column. The mass loadability of an open-tubular LC column and a 21μm micropacked capillary were compared and were found to be in the same range. The optimization procedure uses known and established relationships, describing speed, efficiency and mass loadability in chromatographic systems. The calculations were carried out with a spreadsheet computer program.