High temperatures during reproductive development alter kernel development and reduce yield and quality in wheat (Triticum aestivum L.). Understanding how temperature alters kernel formation will help the development of genetic approaches to enhance heat tolerance in this cereal. A relationship between kernel development and postanthesis cytokinin accumulation is well documented, but the effect of temperature on this relationship is not known. This study quantified the effects of a postanthesis temperature treatment (7 d at 35/25°C day/night) on kernel development and cytokinin accumulation in a soft white winter wheat (c.v. Stephens). Kernels from control plants maintained at 25/15°C accumulated zeatin, dihydrozeatin and their corresponding 9-ribosides from 1 to 4 d postanthesis. Postanthesis kernel cytokinin accumulation was reduced by 50-80% by the temperature treatment. Kernel cytokinin content in control plants declined to baseline by 5 d postanthesis and remained at that level. Kernels from treated plants had a secondary peak of cytokinin accumulation 6-8 d after anthesis. This treatment significantly reduced kernel weight. The magnitude of the effect on kernel number was smaller than on kernel weight, but was statistically significant. Reduced kernel weight was accompanied by reduced cytokinin accumulation. Exogenous cytokinins did not mitigate the temperature effects on kernel weight, but at the highest concentrations, did reduce the effect on kernel number.