The comparative effects on skid resistance of the two commonly used treatments for frost and ice on New Zealand roads, mineral grit and the anti-icing/de-icing agent calcium magnesium acetate (CMA), were examined through an on-road test programme. This involved locked-wheel braking tests on selected test sites under a variety of conditions using an instrumented car. Tests were conducted for various treatments, including dry (no treatment), wet, application of grit and application of CMA. Road surface types included fine and coarse chipseal, open-graded porous asphalt, asphaltic concrete and slurry seal. Comparisons of skid resistance were made between the different surfaces and different road surface treatments. Additional laboratory tests were conducted to assess the comparative variation of skid resistance with time following treatment. Typical traffic levels were also obtained for the test sites. These were combined with the changes in skid resistance for the different treatments at different times to provide an assessment of the relative levels of risk for road users. Some implications for managing the use of CMA and mineral grit were also examined.