The aim of this study was to compare the occurrence of L. pneumophila in hot water samples from hot water tanks and instantaneous devices. Tanks and devices were all operated by heat exchangers employed in the town's district heating system. Thirty-six out of 171 (21%) hot water samples tested positive for L. pneumophila isolation, with 14.6% belonging to serogroup 1 and 6.4% to serogroups 2-14. The proportion of L. pneumophila detected in hot water reservoirs (30%) was higher than that observed in hot water instantaneous devices (6.2%). Differences in L. pneumophila isolation reflected different temperatures registered at the faucet: less than or equal to 50 degreesC for hot water from reservoir devices, and >60 degreesC for hot water from instantaneous devices. These data emphasize the need to control temperature in hot water distribution devices, thus inhibiting the formation of biofilm and L. pneumophila colonization.