SUMMARYThe molecular weight distribution of humic substances in soil solutions from a dystric cambisol and an orthic podzol were determined by high‐performance gel filtration chromatography (Toyo Soda TSKgel G2000 SWXL column). The retention volumes of humic substances were compared to those of narrow molecular weight distributed poly‐styrenesulphonates with known molecular weight.A change in mobile phase pH or ionic strength usually resulted in an almost identical change in retention volume for the polystyrenesulphonates and the bulk of humic substances. The possibility of using the former to calibrate the column is discussed. The molecular weight at peak maximum was 1120–1190 and 1800 for the cambisol and podzol samples, respectively, using polystyrenesulphonates as molecular weight standards. No pretreatment of samples was used, but ion exchange is recommended for samples with high Al concentra