SummaryThe effect of pH on the incorporation of six14C‐labelled amino acids and a dipeptide into humic acid extracted from a podzolic soil was examined. Maximum incorporation was found to occur at a pH which coincided with the apparent dissociation constants of their α‐amino groups. Incorporation took place, into forms which were both acid‐hydrolysable and non‐hydrolysable, the latter accounting for between ten and twenty per cent of t