Recently, attention has focused on the effects of weather conditions and seasonal changes on the incidence of acute microcrystalline events. Acute gout attacks are more frequent during the spring, but seasonal variations in the incidence of acute pseudogout attacks are less clearly defined. Genetic analysis of two unrelated families with calcium pyrophosphate dihydrate (CPPD) crystal deposition disease showed linkage to the short arm of chromosome 5p. Several recent reports show CPPD crystal disease occurring in association with Gitelman syndrome, the hypocalciuric-hypomagnesemic variant of Bartter syndrome. Two signaling pathways, protein kinase C and adenyl cyclase, modulate generation of extracellular pyrophosphate by porcine cartilage chrondrocytes. These transduction mechanisms may provide potential targets for the treatment of CPPD crystal deposition disease. A controlled clinical trial showed ultrasound therapy to be beneficial in the treatment of symptomatic chronic calcific tendinitis of the shoulder. There is evidence that apatite crystals may contribute to cartilage damage in osteoarthritis and that therapeutic interventions to prevent the formation and biologic effects of the crystals may potentially retard the progression of the osteoarthritic process.