*Work done at Department of Plant Pathology, Faculty of Agriculture, University College, Belfield, Dublin 4, Ireland.
Conditions for obtaining high yields of viable protoplasts from leaf mesophyll tissue of several Irish potato cultivars were determined. Plant and leaf age had a significant effect on protolast isolation. In general 40–60 day old plants and leaves from positions 4–7 from the top of the plants gave good results. Plants younger than 40 days resulted in poor yields. Pre-conditioning of leaves had a marked effect on protoplast isolation. A 0.1% concentration of macerozyme was optimum for the five cultivars tested. The cellulase concentration varied and best results were obtained with 0.3% cellulase for cvs. Golden wonder and Home Guard and 0.5% for cvs. King Edward, Pentland Crown and Pentland Dell. Isolated protoplasts were cultured on several test media and viability was at least 5% on four of the media tested and plating efficiency varied between 10.7 and 40.2%. These protoplasts underwent cell division and formed calli.
