In this paper we present an approach to tracking of humans in spaces with ubiquitous distributed sensors and actuators - Intelligent Spaces. In order to be able to implement services that depend on the position of humans, a reliable tracking method is needed. In addition to the sensors distributed in space, mobile sensors are also considered. A mobile sensor is a mobile robot equipped with onboard sensors, which can be used to improve the estimate. Here we present an implementation based on laser range finders and track the position of humans, as well as the mobile robot, using a Kalman filter. Characteristics of such a tracking system are analyzed and experimental results are shown.