In the past ethnological objects were treated extensively with highly toxic arsenic and mercury compounds and chlorine-containing pesticides. Consequently, they are the source of considerable air and dust pollution in ethnological collections. They create a handling problem, are very difficult to store and to exhibit. Normal cleaning techniques with solvents cannot remove the embedded residues from the pesticides that still remain in layers near the surface. However, liquid carbon dioxide (L–CO2) as a solvent came to our attention due to successfully studies with supercritical carbon dioxide. Experiments with L–CO2 showed a good cleaning effect on ethnological objects, and oils from excessively lubricated works of art were satisfactorily removed. The decontamination rates for DDT (91%), arsenic (25.5%), and lindane (15.4%) vary in order to the materials and substances. Yet, no results were achieved for pentachlorophenol and mercury compounds. This work aims at finding the right conditions for effective pesticide-extraction and for the cleaning and degreasing of ethnological objects without any damage. Our current research in using L–CO2 for cleaning pesticide-contaminated objects seems to be a very promising method, compared to alternative potential treatments making use of organic solvents. L–CO2 holds promise as a decontamination method and as an interesting alternative to the high-pressure extraction with supercritical carbon dioxide (SC–CO2), which is costly and technically more complex to carry out. With the use of the liquid phase of carbon dioxide, “Green Chemistry” finds its way into conservation science. Since pesticide-contaminated collections are a worldwide problem there is an urgent need to carry out more studies in this field.