The aim of this paper is to evaluate the reliability of ryegrass species as active biomonitors by assessing atmospheric metal concentrations. We show a procedure for measuring atmospheric concentrations of heavy metals by means of biomonitors and present the data collected between July 1997 and October 2000 in the industrial area of Tito Scalo (Basilicata region, Southern Italy). In particular, we discuss the reproducibility of the biomonitoring measures, the influence of plant age and the correlation between metal concentrations in plants and in atmospheric particulate. Statistical analysis of measured data suggests us that in the investigated site, Cd, Cr and Ni are suitable to be monitored by means of ryegrass species. For the other metals, their emission patterns in atmosphere make it difficult to identify the correlation structure between plants and particulate, and as a result the interpretation of the biomonitoring data is complex. On the basis of the results, we believe that for correct application of active biomonitoring procedure, a careful preliminary analysis of the monitoring site and integration of the biomonitoring and chemical-physical observation is necessary.