The erythrocyte sedimentation rate (ESR), now more appropriately referred to as the "length of sedimentation reaction in blood (LSRB)", remains the most widely used laboratory test for monitoring the course of infections, inflammatory diseases and some types of cancer. Thanks to the several recently developed methods for the measurement of this reaction, the safety and reliability of LSRB testing procedures have improved. The method for LSRB measurement recommended by the International Council for Standardization in Hematology (ICSH) and the National Committee for Clinical Laboratory Standards (NCCLS) is based on the traditional Westergren method, using EDTA-anticoagulated samples. The present paper describes and evaluates a procedure for LSRB measurement with a new manual system, the Microtest 1, which requires only 30 microl of blood and is optimal for pediatric use. Microtest 1 results correlated satisfactorily with the ICSH recommended method (r=0.88, 95% CI 0.84-0.91; y=3.45+0.85x), had no significant bias (2.15, 95% CI -0.32-4.63) and had an imprecision of less than 7% for the reference range values. In addition, the results obtained with the Microtest 1 in "native" whole blood were comparable with those obtained with the reference method in K3EDTA and sodium citrate-anticoagulated specimens; (bias = 1.19, 95% CI -1.78 to 4.16 for K3EDTA-anticoagulated samples and bias = 2.43, 95% CI -0.58 to 5.44 for sodium citrate-anticoagulated samples).