Extracts from unsterile sheep fleeces seeded with Pseudomonas aeruginosa, Proteus mirabilis, Enterobacter cloacae or Bacillus subtilis equally stimulated oviposition by females of Lucilia cuprina (Wied.). However, with increasing length of incubation, significant differences emerged, the cultures of P. mirabilis, E. cloacae and B. subtilis becoming contaminated with increasing numbers of Pseudomonas aeruginosa and the responses of the flies to the culture extracts becoming greater. The maximum number of eggs was laid over four–g day–old cultures. The response was highly significant for Proteus mirabilis and E. cloacae but not significant for B. subtilis. Although contamination with Pseudomonas aeruginosa appeared to be the cause of the increased oviposition, pure P. aeruginosa cultures did not elicit high responses. The response to cultures of P. aeruginosa was apparently enhanced by interactions with other bacteria.