The geochemical study of pyroclastic cones and flows of the Ser basin (Olot Volcanic Field, NE Spain) shows significant compositional differences among the volcanic centers and flows. The seven cones sampled are typically alkaline (basanite, alkali olivine basalt and potassic trachybasalt). By contrast, the eastern part of the flows (farthest from the emission centers) contains hy-normative olivine basalts (subalkali olivine basalts, no ne-normative). This flows seems to be covered by younger alkali flows and pyroclasts. Two of the cones are made of rocks coming from slightly evolved alkaline basaltic magmas (close to phonolitic basanites). The olivine basalts from the eastern flows are not in the alkaline trend of differentiation observed. On the contrary, its origin may be related to a higher degree of melting in the mantle