The effect of delayed entry (2-48 h) into BacTAlert 3D and BACTEC 9240 and the effect of 2 storage temperatures (22 degrees C vs 35 degrees C) on bacterial growth was evaluated. The delay in transportation of blood culture bottles stored at room temperature had no effect on the recovery rate for the first 12 h. Culture positivity was between 74.4% and 100% for different microorganisms at less than 24 h preincubation time. The positivity rate decreased significantly for Acinetobacter baumannii, Bacteroides fragilis, Escherichia coli, Enterococcus faecalis, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Streptococcus pneumoniae for more than 24 h of delay. Culture positivity was higher at 22 degrees C for all microorganisms especially for Enterococcus faecalis and P. aeruginosa. Effects of instrument, preincubation time, and temperature showed that the risk of culture negativity increased 1.5 times for BACTEC compared with BacTAlert 3D and increased 2.5 times for 35 degrees C compared with 22 degrees C. The negativity increased 5.5 times and 8.5 times at 24 and 48 h of delay respectively, compared with no delay.