After the International Agency for Research on Cancer (IARC), Lyon classified crystalline silica within Class I, i.e. substances for which there is clear evidence of carcinogenicity to man, the need was felt for further studies to quantify the concentration levels and ensuing risks the general population is exposed to. Crystalline silica is a well-known pollutant which has been largely dealt with in literature as far as occupational exposure is concerned. On the contrary, the data resulting from environmental studies are scarce and usually inadequate, hence the importance of determining the levels of quartz (the most common form of crystalline silica) in the respirable fraction of the airborne particulate in urban areas in a reliable way. This paper is the continuation of a previous study which reported data on quartz concentrations in PM10 collected in an urban site of the metropolitan area of Rome in 1994 (the first year PM10 started to be collected). Measurements had been made with a new procedure that involved the use of X-ray diffractometry and silver filters, permitting the reproducible quantification of small amounts of quartz in the urban atmosphere. In the present work we report the mean daily quartz concentrations in PM10 collected for four weeks representative of the four seasons, from May 1997 to February 1998, in the same sampling site as in 1994. We then compare the two sets of data; in addition, we report preliminary estimates of the potential risk of contracting lung cancer for the general population.