of 1,234 subjects eligible at baseline, 1, 041 (84.4 per cent) participated in thebase- line examination of risk factors; 892 73.3 percent) also completed questionnaires. Of baseline participants, 432 (41.4 per cent) were available for re-screening after two years of intervention, forming the cohort At two years similar across groups. Signif- icantly more males, lower SES, and older students in control group. Females were more likely to be available at the 2 yr fol- low-up (P< 0.05). Serum thiocyanate in the baseline cohort was 34.2 umollL and 33.3 In those lost to the 1 yr follow-up (P 0.41). High attrition due to transfers to other schools