an earlier epidemiologic and electron microscopy study of drinking water in the everett area of washington state indicated large numbers of naturally occurring chrysotile asbestos fibers in the water . 
 the purpose of the present study was to determine whether significant numbers of asbestos fiber could be demonstrated in the urine of donors residing in that area for less than 3 yr and over 20 yr where the tapwater contained about 200 x 10(6 ) fibers / l . 
 a control group was obtained from seattle where the tapwater asbestos fiber content was 100 times less . 
 urine samples , filtered control water , tapwater samples , and additional controls were processed for transmission electron microscopy by the use of the nuclepore membrane filter - jaffe wick procedure . 
 interference by mucus in the urine was reduced by treatment with hydrogen peroxide . 
 samples were taken over a period of 21 months . at no time during this period did the asbestos content of the urine samples consistently exceed that of the control waters . there was a significant difference ( p less than 0.05 ) in the asbestos content of urine samples from subjects with less than 3 yr residence times versus greater than 20 yr . asbestos concentration in urine samples from everett residents as a whole did not differ significantly from that in samples from seattle residents . 
 variable degrees of chrysotile contamination of control water samples and of nuclepore membrane filters presented a problem . at present , the data are inconclusive but would suggest no relationship between high concentrations of fibers in drinking water and the numbers estimated for voided urine.imagesfigure 2.figure 3.figure 4.figure 5.figure 6 .