X-ray powder diffraction, infrared spectroscopy and thermal analysis were used to study 108 stones that had been passed spontaneously from the upper urinary tract. The presence of apatite in pure calcium oxalate stones classified by x-ray diffraction was confirmed by infrared analysis of the ignited product. Consequently, 102 of 108 stones were found to be composed of weddellite and/or whewellite, and apatite. Besides the contents of weddellite, whewellite and apatite, the content of organic matrix also was estimated by thermal analysis in 102 stones, ranging from 1.1 to 17.2 per cent. The stones then were divided into 3 groups according to the principal constituent: 1) weddellite, 2) whewellite and 3) apatite. Weddellite stones were significantly heavier and significantly higher in apatite content than whewellite stones. It is suggested that weddellite calculi tend to become larger than whewellite stones. The apatite content was correlated with the ratio of weddellite to weddellite plus whewellite ( r equals 0.528), and the content of organic matrix was correlated with the whewellite content (r equals 0.708). Thus, it is considered that the weddellite-apatite and whewellite-organic matrix associations have important roles in the development and growth of weddellite and whewellite calculi, respectively.