This report describes a system for monitoring bicycle activity in sequences of gray scale images from a stationary camera. Applications for such a system include determining the use and congestion of bicycle paths. The output of the system is a count of the number of bicycles detected in the image sequence. The system uses a simple model of two circular objects separated by relatively known distance, with four levels of abstraction: raw images, blobs, edge images, and the bicycle model. The system was implemented on a dual Pentium computer equipped with a Matrox imaging board and achieved a peak performance of eight frames per second. Experimental results based on outdoor scenes show promising results for a variety of weather conditions.