The infectivity to mouse macrophages and sandflies, the expression and enzymatic activity of the major surface glycoprotein (gp63), the developmental modification of lipophosphoglycan (LPG) and three metacyclogenesis markers (promastigote body size, lectin agglutination and complement resistance) were compared in four related Leishmania major promastigote lines. The lines, which differed in their virulence for BALB/c mice, were examined in both logarithmic and stationary phase. Although the two non-virulent lines were unable to survive and multiply within the macrophages, they were better at attaching to the macrophages and infecting sandflies than the two virulent lines, which were highly infective for macrophages. Except for the higher resistance of the attenuated parasites to complement-mediated lysis, there were no clear differences between the metacyclogenesis markers of the four lines. The amount and enzymatic activity of surface gp63 was relatively high in the attenuated promastigotes and this appears to be related to a higher expression of gp63 genes. In terms of LPG, cells of all the lines had approximately twice the number of galactose and mannose residues per molecule when in logarithmic phase than when in stationary phase. LPG of the virulent lines also contained approximately twice the mannose and galactose residues of the attenuated line. Although L. major gp63 could therefore be important for promastigote survival in the sandfly and for the resistance to complement-mediated lysis, there was no apparent correlation between gp63 expression and promastigote survival in the macrophage. A very elongated LPG could be necessary for the survival and proliferation of the parasite in macrophages.