During an 8 month period, 298 evaluations of direct and buffy coat films of peripheral blood for the detection of bacteraemia were undertaken in 287 infants (243 less than 24 h of age and 55 aged between 2 days and 30 days). Bacteraemia was diagnosed by simultaneously drawn aerobic and anaerobic blood cultures. Intracellular organisms were observed in both the direct and buffy coat films of only four of 24 infants with bacteraemia, giving a sensitivity of 17%, specificity of 100% and positive and negative predictive values of 100% and 93%, respectively. Of 12 infants with bacteraemia on the first day of life, eight were asymptomatic when studied, and none of the 12 had positive smears. As two of four infants with positive smears died, it is concluded that in fulminating sepsis the tests seem to correlate with the degree of illness and may give useful information as to the causative organism and the choice of antibiotic. However, as a screening test, the present methodology lacks sensitivity and cost-effectiveness.