Wheat (cv. Gabo) was grown in a controlled environment and supplied with various levels of calcium and phosphate. Low levels of phosphate accelerated maturity irrespective of calcium concentrations, while high phosphate levels delayed maturity. The converse applied to calcium concentrations, and phosphate effects tended to dominate those of calcium. The maturity effects partly explain the lower lignin content of plants grown with high levels of phosphate observed by other workers.Plants were harvested at the same level of maturity, viz. when the top inter· node had completed elongating. The top three internodes were analysed for calcium, phosphorus, lignin, and peroxidase.The internodes of plants grown with higher levels of phosphate contained greater amounts of phosphorus. Internode calcium, however, did not increase above a certain value irrespective of nutrient concentration. Unlike phosphorus, internode calcium was relatively immobile.Low·calcium plants contained the most lignin, but only with low phosphate treatments. The lignin content of medium and high calcium treatments was not significantly different. Increasing the phosphate level with medium and high calcium levels reduced lignification. Peroxidase specific activity was lower in low and high calcium and phosphate treatments than in controls, but there was no correlation between this activity and lignin content.Plants grown with low calcium levels had a significantly higher percentage of total peroxidase attached to the internode cell walls than other treatments. Phosphate levels did not affect the amount of wall-bound peroxidase. The percentage of soluble protein loosely bound to cell walls did not differ significantly between treatments.Phosphate apparently modifies lignification by affecting maturity, but also by some other means. Increasing the levels of calcium probably reduces lignification by releasing peroxidase from the cell wall. Phosphate effects again dominated those of calcium.