Defines a method for the determination of the total polyethylene glycol (PEG) content of aromatic and aliphatic non-ionic surface active agents of the type R-(O-C2H4)p-OH, where 'p' is the mean ethylene oxide (EO) value. Applicable for concentrations of PEG higher than approximately 0,1g/100g of the laboratory sample. Applicable to a degree of ethoxylation of at least 25 for products which are soluble in an 80/20 (V/V) mixture of methanol and water. Long-chain products with a low degree of ethoxylation, such as tallow alcohol 5 EO, are not soluble, and require an enamelled preliminary treatment.