The author describes the technique for testing a chemical compound for fungicidal activitiy and determining its persistence in an organic coating under different climatic conditions. When formulations had passed these tests they were subjected to field trials in houses which had a history of mold growth and in a brewery over a bottle washing machine. Paints containing copper 8-hydroxy-quinolate and those containing tetramethyl thiuram disulfide showed good results; zinc oxide was not effective in these field trials nor was N-trichloromethylthiophthalimide as a fungicide. The author lists 4 ways in which fungicide can disappear from a paint film. 1) by reacting with components of the paint or the atmosphere (e.g.: H2S), 2) by evaporation if the compound is volatile, 3) by decomposition due to solar radiation, 4) by leaching out in rain or dew. -- AATA