Pigeon pea (Cajanus cajan (L.) Millsp.) cv. T21 was grown in refined sand at manganese levels ranging from 0-0011 to 5·5 mg 1−1. At less than 0·055 mg Mn 1−1, growth was depressed. In manganese deficient plants, there was reduction in the area and number of leaves. A reduction in seed yield was observed at low and excess manganese and was optimum at 0·55 mg Mn1−1. Manganese deficient plants showed enhanced levels of peroxidase and ribonuclease activity and caused reduction in chlorophyll content, sugars, Hill activity and activities of catalase, acid phosphatase and aldolase. When manganese supply was low, manganese concentration in leaves decreased and iron, zinc, copper and phosphorus concentrations increased. Values for deficiency, threshold of deficiency and toxicity of manganese in leaves were respectively 25, 39 and 190·5 μg g−1 and in seeds they were 10·6, 12·8 and 18·2 μg g−1 dry matter.