. We present results of an analysis of new observations of the active M dwarfs AD Leo (GJ 388) and EV Lac (GJ 873), performed with the X-ray satellite SAX, and compare them with both published and new analyses of ROSAT PSPC observations of these stars. The PSPC spectra can be fitted with one- (EV Lac) or twocomponent (AD Leo) isothermal mekal models, and very low metallicity (¸ 0.1 solar); we have found clear evidence of spectral variations in correspondence of a large flare observed during one of the PSPC observations of EV Lac, requiring the addition of a second component with log T ¸ 7.5 to fit the flare spectrum. The SAX light-curves of AD Leo and EV Lac also show the occurrence of several flares. A two-component model does not provide an adeguate fit of the SAX spectra, regardless of the value of coronal metallicity. These spectra require at least three thermal mekal components and best-fit coronal plasma metallicity below solar for AD Leo and only marginally below solar for EV L...