Two solution culture experiments were conducted to study the effects of toxic concentrations of H+ and aluminium on nonsymbiotic growth of groundnut (Arachis hypogaea L.) cv. Matjam. The five pH levels used were 3.5, 4.0, 4.8, 5.5 and 6.5, and the sum of activities of monomeric Al species (2&Almmo) were 0, 1.5, 3.0, 15, 35 and 80 µM at pH 4.3. The H+ ion concentration at pH 3.5 did not affect top dry weight but markedly decreased root dry weight and length. Raising the solution pH to 4.0 improved the growth of roots. The pH level recommended for growth of groundnut was & 4.4. The non-toxic concentration of aluminium for growth of groundnut and rootelongation was ^ 12.2 fiM 2aAlmono (= 17.1 JJLM monomeric-Al or 20.3 /JLM monomeric total-Al). Increasing the ?alm Almmo to 80 fiM decreased the magnesium concentration in the youngest expanded leaf (YEL) to 0.18%, a value known to be deficient for groundnut. Magnesium concentration in the YEL was more sensitive to aluminium toxicity than magnesium concentration in the roots. The results also showed that root dry weight and root length responded positively to low concentrations of aluminium (1.5 µM ?alm(mo); this effect was not observed for dry weight of tops.