The Pacific deep-sea bottoms are dominated by rhizopodan Protozoa. Their abundance on manganese nodules and in the associated sediments suggests a contribution t o nodule formation, though direct evidence is still lacking. Attention is called to iron contents in solid excretion products of some sessile rhizopods that may contribute t o the initiation of manganese deposition and nodule growth. Manganese is scarce in the faecal pellets of sediment-dwelling rhizopods. This is discussed in context with questions regarding manganese mobilizat,ion in pelagic sediments.