Heat stress in dairy cows is an increasing problem because of climate change. Even though South Africa has a warm to hot climate, little research on this topic has been done locally. Currently, while intensive housing is increasing being used in large dairy production systems, a shade structure provides the first step to protect cows against heat stress improving production performance and welfare. This paper provides results on the production performance, physiological parameters and behaviour of Holstein-Friesian cows with and without access to a shade structure during summer. The effects of heat stress on primiparous Holstein-Friesian and Jerseys cows in a breed comparison study are also shown. The milk yield of Holstein-Friesian cows with access to shade was significantly higher than that of cows without shade. Although the difference in milk yield was small (5.5%), the difference between the accumulative milk yield between shade and no shade cows increased over time for each of the three summer seasons, indicating a decreasing ability of cows without shade to withstand heat stress conditions. The internal rate of return on the capital outlay for the construction of a shade structure showed a positive return on investment within three summer seasons. Jersey cows displayed a higher tolerance to heat stress than Holstein-Friesian cows suggesting that they would be more suitable for a hot environment. However, the large difference (ca 30%) in production performance should be taken in account when considering a change in breed. Ways to alleviate the effect of heat stress on dairy cows are suggested.