The imaging properties of optical microscopes can be severely compromised by specimen-induced aberrations causing degraded resolution, reduced signal levels, and image distortion. This is particularly the case in high-resolution, three-dimensional techniques, such as scanning confocal or multi-photon fluorescence microscopy - techniques used extensively in the biological sciences. The aberrations are caused by spatial variations of refractive index within the specimen itself. In wide-field microscopes, this gives rise to aberrations that change across the field of view; in scanning microscopes, they cause temporal variations as the focal spot is scanned through the specimen. The application of adaptive optics to this problem has obvious potential and the principle has been demonstrated in scanning microscopes. To characterise the optical properties of specimens and determine the requirements for adaptive microscopes, we have performed the first detailed study of biological specimen-induced aberrations using an interferometer incorporating high NA microscope objectives. We show that low order correction of aberrations produces significant recovery of signal and resolution and we compare the performance of different correction devices, e.g. deformable and segmented mirrors, for imaging such specimens. It is also shown that that the presence of tip, tilt and defocus modes leads to three-dimensional image distortion that is not easily removed by an adaptive correction system.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.