Yersinia strains either urease-positive or urease-negative were examined for precipitation of struvite in human urine at 25 and 37 degrees C. All urease-positive strains and 8 out of 10 urease-negative strains showed the ability to produce these crystals. Incubation time required for precipitation was longer for urease-negative strains and quantity of struvite formed was higher in urease-positive ones. Regarding incubation temperature, no significant influence has been observed.