Storage of partially processed lettuce resulted in an increase in microbial population, pH, and change in package atmosphere composition (increasing CO2 and decreasing O2). Microbial populations varied in size with variations in processing and packaging. Typical initial log10 counts per g were: bacteria 3.4–5.1, yeasts 2.5–3.2; molds were infrequent. Commercial packaging inhibited bacterial growth and retarded browning. Although Gram-negative bacteria were numerically dominant, a large yeast population was also found. Species in the genera Pseudomonas, Erwinia, and Serratia were the most frequently isolated bacteria. Cryptococcus, Pichia, Torulaspora and Trichosporon spp. were the most common yeasts.