Urine samples were inoculated with viable Proteus mirabilis or purifie
d Jack bean urease. The subsequent pH increase and crystallization wer
e followed for 2 weeks. Particle formation was detected much earlier a
nd at a lower pH in urines inoculated with Proteus, in which a higher
end pH was also reached. The crystal configuration in bacteria and ure
ase inoculated samples was different. Crystal aggregation was also muc
h more pronounced in the Proteus mirabilis inoculated samples. The tot
al precipitation was markedly increased in the Proteus mirabilis inocu
lated samples. The presence of live Proteus mirabilis thus has a profo
und influence on urease-induced crystallization in human urine. Despit
e the formation of rather large crystal aggregates in the Proteus-inoc
ulated urines, no firm aggregates of a ''prestone'' type were observed
.