The participation rate in a maternal serum screening for trisomy 21 was 84% in the Helsinki trial. Six hundred and twenty-five mothers who had a positive result and a random sample of 245 mothers who had a negative result took part in the opinion survey. Ninety-five percent of the first and 97% of the second group considered the screening tests as very or quite useful. However, 12% of those with a positive result would decide against taking the test if they could reconsider, whereas 100% of those with a negative result would take it again. Too little information about the test, worries and stress, unnecessary in cases of false timing, difficult decision-making, and anxiety while awaiting the results of the chromosome study were the main complaints. More information at all stages, earlier testing, ultrasound timing before the serum test, and fast results were considered essential.