The stability of a liquid preparation of free base L-Lysine (L-Lysine concentration 50 per cent) was tested under conditions of feed processing with expander at 90, 110 and 130 degrees C in a growth trial with broilers from 8 to 35 days of age. Non-expanded feed resp. application of the liquid lysine post expanding served as control. Total dietary lysine content was set at 1.00 per cent (90 per cent of NRC 1994; 77 per cent of Austic 1994 recommendation) to make lysine deficient diets. Two wheat-soyabean meal diets, without and with molasses addition have been studied. In diets without molasses addition the treatment at 90 degrees C resulted in the same performance as with the untreated feed resp. the feed with post expanding application of the liquid lysine. The treatment at 110 and 130 degrees C caused reduction in liveweight gain but no differences in feed conversion rate. In the diets with molasses addition the increase in processing temperature showed reduction in feed intake combined with a non-significant decrease in liveweight gain. Feed conversion rate demonstrated a high level of lysine efficiency even after high processing temperatures. Apparent faecal digestibility of total dietary lysine was high (89.01 per cent plus minus 1.27) and N-retention, calculated from carcass analyses did not differ significantly between treatments. Addition of molasses to the diet did not decrease availability of dietary lysine. The results lead to the conclusion that free base liquid L-Lysine is stable under the tested High-Temperature-Short-Term feed processing conditions.