This report provides a description and evaluation of the indirect fluorescent-antibody technique for serotyping and detecting Haemophilus pleuropneumoniae. The indirect fluorescent-antibody technique was serotype-specific when reference strains and sera were tested. Sixty-five field isolates were serotyped by indirect fluorescent-antibody technique and belonged to types 1,2 an 5. Two isolates did not fit any of the five established types. Twenty-three of the 65 isolates were also typed by immunodiffusion and the two tests agreed completely. Haemophilus pleuropneumoniae was detected in freshly-fixed impression smears from 12 lungs having acute pleuropneumonia. The identity of the bacteria was subsequently confirmed by cultural procedures. Fixed smears of cultured Haemophilus bacteria can be stored or mailed at -20 degrees to +24 degrees C without losing stainability.