The electrical resistivity of Pt-Mn alloys containing from 0.09 to 18% Mn has been measured. In the most dilute alloys, a clear logarithmic region of positive slope has been observed in plots of resistivity against temperature, indicating that these Pt-Mn alloys show Coles-like behaviour. In all alloys up to about 11 at% Mn a resistance minimum has been observed which is attributed to spin glass ordering, below the minimum the resistivity follows the general T^3/2 law associated with spin glasses at low temperatures. Above this concentration there is no minimum and the resistivity is found to increase monotonically with temperature.