The MicroScan MICroSTREP MIC panel was compared with PASCO and Sensititre systems against 157 isolates of Streptococcus pneumoniae chosen to include penicillin-susceptible, intermediate, and resistant strains. Arbitration testing was performed by microbroth dilution using National Committee for Clinical Laboratory Standards guidelines. Overall essential agreement of 94-97% and categorical agreement of 91-94% with the reference method was achieved for the three systems. There were 8 very major errors (false susceptibility) for PASCO, 10 for Sensititre, and 9 for MICroSTREP; 4 major errors (false resistance) each for PASCO and MICroSTREP, and 6 for Sensititre. Most of these errors occurred with trimethoprim/sulfamethoxazole. Minor errors (susceptible or resistant versus intermediate) totaled 47 for PASCO, 69 for Sensititre, and 53 for MICroSTREP. Minor interpretive errors were most common with penicillin and ceftriaxone. This study showed that all three MIC panels provided interpretive results comparable to one another and to the reference method. Copyright (C) 1999 Elsevier Science Inc.