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SUMMARY The behaviour of the metal chelates M n -E D T A , M n -D T P A , M n -E D D H A , F e -E D T A , F e -D T P A and F e --E D D H A in calcareous soilsand their availability to plants were studied.The effectiveness of a m e t a l chelate was shown to depend on its stability, the fixation capacity in the soil and its toxicity to the plant. Incorporation of F e -D T P A into a framework of silica molecules prevents the fixation of F e -D T P A in the soil.F e -D T P A and F e -E D D H A cause a reduction in the manganese uptake of the plant.The most striking result was the behaviour of M n -D T P A in calcareous soils. Partial replacement of manganese in the chelate b y iron Irom the soil makes this chelate useful for supplying the plant with both iron and manganese. M n -D T P A appears to be the ideal type of chelate for the correction of chlorosis in the Netherlands, but unfortunately is not yet commercially available.