Force curves have been acquired using an atomic force microscope (AFM) on homogeneous microspheres of three different materials (latex, glass and yttria), in order to study the possible influence of the surface topography/geometry on the adhesion force as measured by an AFM. Forces were measured in regions at the top of the spheres (theta approximate to 90degrees), at half-heights (theta approximate to 0degrees) and in an intermediate region between these two (theta approximate to 45degrees), where the angle theta is measured from the equatorial plane of the sphere to its polar axis. A very irregular and non-reproducible behaviour was found at theta approximate to 0degrees, so only the other two regions were quantitatively analysed. For all the three materials, a much smaller adhesion force was obtained in the region corresponding to theta approximate to 45degrees as compared to theta approximate to 90degrees. Moreover, a quite similar adhesion decrease ratio of about 1.60 +/- 0.5 was obtained for all the three materials, which may suggest that the observed behavior might be due to geometrical factors. This observed influence could, in part, explain the observed heterogeneity in adhesion maps of microbial cells reported in the literature. The influence of the surface roughness is also discussed and it seems to result in a poor reproducibility of force curves.