Metal constituents of filters collected from 1996 through 1998 from five monitoring network stations of Mexico City, were identified using ionization argon coupled plasma. Nine metals were quantified: cadmium, chromium, copper, manganese, nickel, lead, titanium, iron and vanadium. The statistical analysis shows that in general the metal concentration diminished from 1996 to 1998 in total suspended particles and PM10 although there are some exceptions. The correlation between TSP and PM10 shows that there is a higher proportion of metals in the respirable fraction than in the particles with bigger diameter. Lead content did not exceed the standard concentration of 1.5 mug/m(3); with an average value of 0.09 in PM10 and 0.17, in TSP and the highest values of this metal were 1.03 and 0.96 for PM10 and TSP, respectively, both in January of 1996. The study of size and shape by scanning electronic microscopy led us to identify particles from natural soils and clays, from combustion and from industrial processes.