Fertilizers containing the condensates of urea and specified aldehydes (with crotonaldehyde called crotonyliden diurea or CDU, with isobutyraldehyde called isobutylidene diurea or IBDU, with formaldehyde called urea formaldehyde or methylene urea or MU) are covered by Annex I of the Regulation (EC) 2003/2003 [1] as nitrogenous fertilizers. The methods described in this European Standard enable the quantitative determination of these condensates and the determination of the solubility of the MU-oligomers according to the Regulation.