Aims-To establish a simple method of quantitative culture for determin
ing the viable bacterial numbers present in expectorated sputum sample
s. Methods-Sputum samples were homogenised with dithiothreitol, steril
e saline or glass beads to determine which method recovered the greate
st number of viable bacteria. Culture broths were also incubated with
dithiothreitol and sampled over time to determine its effect on bacter
ial viability. Sputum samples homogenised with dithiothreitol were dil
uted in sterile saline and sampled using either standard bacteriologic
al loops or a precision pipette to determine which method resulted in
the least variation. Results-Homogenisation of sputum using dithiothre
itol increased the recovery of viable bacteria compared with sterile g
lass beads and/or saline, with no apparent effect on bacterial viabili
ty when incubated with culture broths. By inoculating agar plates with
10(-3), 10(-4) and 10(-5) dilutions of the homogenised sputum sample,
all potential pathogens could easily be identified. A 10 mu l sample
volume dispensed by precision pipette and spread with a ''hockey stick
'' resulted in the least variation between plates (less than 16%) and
an even distribution of bacterial colonies. Numbers of viable bacteria
recovered from different aliquots of individual sputum samples were g
enerally of the same order of magnitude. Conclusions-This method repre
sents a relatively quick and simple technique for accurately quantifyi
ng viable bacteria present in sputum samples. The use of a small porti
on appears to be representative of the sample as a whole.