Many large power/petrochemical plants have older cooling towers which are in need of major repairs but shutting down these towers will result in large production losses. A project was started in which the water distribution system and the splash pack grids of four existing natural draft cooling towers at a large petrochemical plant were to be replaced without shutting down the water flow to the cooling towers. The water flow to typically 10% of a given tower was shut off after the installation of butterfly valves. The existing packing in this area was then removed and replaced with new high performance slash packing. The work on the first two towers is scheduled for completion in July 2004. Performance tests on these two towers are scheduled for the southern hemisphere summer 2004/2005. The work on the remaining two towers is scheduled for completion at the end of 2005.