['To evaluate the reliability and criterion-related validity of a revised version of the reference-based protocol for manually assessing lumbar posteroanterior (PA) stiffness. With the revised protocol, a therapist matched the stiffness of the spine to 1 of 11 stiffness references provided by a mechanical device.', 'Two physiotherapists and 41 asymptomatic subjects participated.', "Subjects' PA stiffness was assessed by the therapists and the Stiffness Assessment Machine(criterion measure) under standardized conditions. The therapists pressed on the subject's spine and then the mechanical device, the task being to match the stiffness of the back to 1 of the 11 stimuli provided by the device. Each of the 11 stiffness stimuli represented a point on the -5 to +5 stiffness scale. Interrater reliability was evaluated with 2-way analysis of variance (ANOVA) intraclass correlation coefficient for a single rating (ICC [2,1]) and the SEM, whereas criterion-related validity was evaluated with the Pearson product moment correlation (r), including the Fleiss correction.", 'The ICC (2,1) was 0.78 (SEM 0.56), and the criterion-related validity reached 0.74 (Fleiss correction 0.86).'] Is objective manual assessment of lumbar posteroanterior stiffness now possible?