OBJECTIVE To evaluate a hand held portable i-STAT analyzer used for point-of-care testing in a hemodialysis unit. METHODS Imprecision and comparison studies. Assays by nonlaboratory personnel. RESULTS Study of both quality control solutions and hemodialysis patients' duplicate blood specimens with 6+, E3+, EC6+, and EC8+ cartridges both gave CVs for sodium, potassium, chloride, pH, and ionized calcium of 0 to 2.2%. CVs for hematocrit, glucose and pCO2 for whole blood duplicates were 4.6, 3.5, and 4.0%. The mean differences between i-STAT and central laboratory values for the above compounds and urea, when expressed as a % of mean central laboratory values were 0.2 and 3.1%, except for an ionized calcium value of 4.3% (for which there is an explanation) and for glucose (11%) that were both higher for i-STAT. Preliminary data suggest that sodium, potassium, ionized calcium, and pH can be assayed in the aqueous dialysate fluid used for hemodialysis. CONCLUSIONS We confirm previous reports that i-STAT cartridges give simple, rapid, and reliable values for sodium, potassium, chloride, urea, glucose, and hematocrit that are clinically acceptable when performed by nonlaboratorians, but also suggest the same conclusions apply to ionized calcium, pH, and pCO2. The hemodialysis unit may prove to be one of several hospital units where the analyzer has considerable value.