Two commercially available baby milks, one 'biologically acidified', the other 'non-acidified', and a traditional weaning food, millet gruel, were prepared and stored under village conditions in West Africa. Increases in total colony count and in number of Bacillus cereus, Clostridium welchii, Staphylococcus aureus and Escherichia coli were determined in these products when stored as commonly practised at ambient temperatures over a period of 8 h. Poor hygiene during preparation was indicated by readily detectable numbers of coliforms and E. coli in freshly prepared samples of each of the milks, though the cooked local gruel seemed less vulnerable in this respect. The rate of increase in the numbers of these organisms was lower in the acidified milk when prepared with unboiled water containing high numbers of coliforms and E. coli. Increases in total colony count and in numbers of Staph. aureus were also less marked in the acidified milk. When food was not eaten soon after preparation the problem of bacterial overgrowth was as great with the local gruel as with the considerably more nutritious reconstituted milks.