Geographical variation in fresh Aloe ferox leaf exudate of which the dried product is commercially known as Cape Aloes, was investigated throughout the natural distribution range of the species. The composition of the major compounds is remarkably invariable, with aloeresin A, aloesin, and aloin (both epimers A and B) contributing between 70% and 97% of total dry weight, in a ratio of approximately 4:3:2, respectively. Minor compounds are less evenly distributed, with aloinoside A and aloinoside B more frequent in the western parts of the distribution area and aloeresin C and 5-hydroxyaloin A generally present in small quantities throughout the distribution area. The aloin content of the exudate is clearly related to provenance but there are no distinct geographical discontinuities. The selection of high-yielding provenances, with total aloin levels above 25%, is recommended for commercial cultivation.