The main purpose of an operating system is to supply the user programs with persistent, simple and enough powerful service interface. However for practical use of the system it is often necessary to know the current state of the system, how much resources the system is using and which user programs consume the biggest portion of them. In the thesis we discuss the possibilities of the operating system monitoring in common. For HelenOS system (which was missing any monitoring facility) such interface was created. Next to the monitoring services we designed and implemented a simple statistical pro ler. Both the user programs and the whole operating system can be pro led. Two userspace applications were created for this purpose.