Plasma and amniotic fluid amino acids were assayed in 20 women of genetic risk groups in the second trimester of pregnancy. The age of patients ranged from 19 to 38 years. Indication for amnio-puncture were: chromosomal aberration or neural tube defect in previous pregnancy or age of pregnant women over 35 years. Blood and amniotic fluid were obtained with transabdominal amnio-puncture performed routinely in prenatal diagnosis. Amino acids were assayed with ion exchange column chromatography, using automatic amino acids analyzer LKB 4400. The obtained results were compared with plasma and amniotic fluid amino acids patterns in healthy women at the same trimester of pregnancy. The comparison of plasma aminograms revealed increased concentrations (above 100%) of cystine and alanine in the examined group. In women with neural tube defect in previous pregnancy and in those over 35 years of age, increased proline, leucine and valine (above 50%) concentrations were found. Decreased concentrations of glutamic acid (about 60%) was detected in women with chromosomal aberration in previous pregnancy and in those older than 35 years. Amniotic fluid amino acid pattern showed in all three patients groups decreased values arginine and ornitine (amino acids of the urea cycle), and also of cystine and taurine. In women with neural tube defect in previous pregnancy and in those older than 35, decreased concentration of lysine, serine and leucine was found. Also in the above 2 groups increasing tendency in comparison to the values in healthy women was observed for alanine (30-40%) and asparagine (150-215%). No correlation was observed between particular amino acids plasma concentration and amniotic fluid in our patients. Ratios of plasma to the amniotic fluid (P/FA) amino acid concentrations were calculated for the examined group and compared with those in healthy pregnant women. While in the last population most of the analyzed scores is below 1 which points higher amino acid concentration in amniotic fluid than that in plasma, performed analysis revealed; an increase in P/AF ratio by 214% in the group of "neural tube defect" women, alanine, glutamine and ornitine P/AF ratios were 35-50% than the normal value. P/AF ratio for cystine by 176%, for tyrosine--100% and for ornitine and arginine--55-65% respectively higher than normal in patients of "chromosomal aberration". P/AF ratio for glutamine acid was decreased by about 50%. In patients examined because of age above 35 years, P/AF ratio for cystine was increased by 200%, for alanine by 125%, for proline, histidine, ornitine, phenylalanine, I-leucine and metionine were increased by 30%-50%.(ABSTRACT TRUNCATED AT 400 WORDS)