ISSR-PCR was carried out on 12 accessions of the grapevine (Vitis vinifera L.) variety 'Garnacha' and one accession of a related variety. The analysis had two objectives: to determine if ISSR-PCR could detect polymorphisms within a variety unable to be revealed previously with RAPDs, and to quantify the intralaboratory reproducibility of the assay. Two electrophoretic systems and staining procedures were assessed. No intravarietal differences could be detected. However, the ISSR approach revealed highly reproducible polymorphisms among the two varieties tested. The reproducibility of the banding patterns ranged from 86 to 94 per cent, being maximum when polyacrylamide gel electrophoresis and silver staining procedures were followed and weak bands discarded.