The effects of the temperature dependence of properties on laminar natural convection transport from an isothermal vertical surface in water are calculated. Bounding temperature conditions in the range 0–100°C are considered in the laminar boundary-layer equations. Results are compared with those obtained assuming constant properties. Large effects on flow and transport arise. These predictions are in good agreement with the limited experimental data available. For bounding temperatures greater than 20°C, heat transfer is correctly predicted by a constant-property solution to within 5% when the film temperature is used to evaluate properties. Detailed transport parameters are tabulated and plotted over the whole temperature range.