As part of the Eureka Eurolaser definition phase programme Lumonics Ltd have undertaken an experimental work programme with supra-kilowatt lasers. The work, which started early in 1987 has been directed at identifying the practical advantages that might result from the realisation of high power solid-state lasers and which would justify their commercial development. The specific tasks within the Lumonics programme have included, (i) establishing a processing data base with available CO2 and YAG laser sources to provide 'benchmarks' against which to assess improvements, (ii) building experimental pulsed YAG lasers of average power to greater than 2 kW for advanced processing trials, (iii) investigating the feasibility of developing fibre optic beam delivery systems compatible with supra-kilowatt average power lasers, and (iv) determining the practical power limits to solid-state laser technology, eg component life, efficiency, etc. The paper will review the progress of these four key areas within the Lumonics programme. It will cover the processing results obtained with experimental YAG lasers of up to 2.3 kW average power and 35 kW peak power in a beam of approx 170 mm-mrad diameter-divergence product. In particular, the performance in deep penetration welding of stainless steel and mild (low carbon) steel will be reported and will be compared with that obtained with other power sources, eg CW CO2 and YAG beams, e-beams, etc. The conclusions which can be drawn from the work programme will be summarised.