Concentrations of calcium, sodium, magnesium, calcium (total and ionised) and inorganic phosphorus were determined in amniotic fluid. Samples were taken from patients between 42-43 week of gestation (investigated group) and between 38 and 40 week (control group). Micro-methods, generally acknowledged in laboratories of clinical biochemistry were used. In the protracted pregnancies increase of magnesium levels and decrease of sodium levels were observed. No differences in concentrations of calcium, calcium (total and ionised) and inorganic phosphorus between investigated and control group were noted. Independently of the duration of pregnancy, near term or post term, ionised calcium constituted 90% of total calcium in amniotic fluid.