The Paleoclimate Modelling Intercomparison Project (PMIP) investigates the physical mechanisms of climate change. The response of various climate models with different physical parameterizations to uniformly used boundary conditions, which are prescribed by PMIP, is compared. As a participant of PMIP the simulations for 6000 years BP (Climatic Optimum, this Entry_ID), 21000 years BP (Last Glacial Maximum, Entry_ID=ECHAM3_T42_32004K021), and 115000 years BP (Glacial Inception, Entry_ID=ECHAM3_T42_32001K115), additionally a new Control Run with revised insolation (Entry_ID=ECHAM3_T42_32005K000). The time slice of this experiment (6000 BP) is mainly defined by an altered annual distribution of insolation: Enhanced summer insolation over high northern latitudes, reduced northern winter insolation with a maximum in the tropics. This is roughly the opposite insolation pattern to the 115000 BP distribution. The climatological SST, which is a 10 year mean of the AMIP data set, and modern surface boundary conditions were used.