Abstract: This paper describes the design, implementation, and use of a model of sporadic tasks in the Real-Time Mach kernel (MK83). This provides a programming model in real-Time Mach (RT-Mach) that is better suited to the requirements of applications, such as distributed multimedia applications, that must execute in response to non-periodic, but repetitive events. We develop a programming model for real-time systems that allows for the modular construction of real-time applications as a set of cooperating processes where the real-time performance of an application is invariant of its structure. We also develop a new result in the theory of sporadic tasks that is used to greatly simplify the implementation of sporadic tasks.