We have identified different beta-thalassemia mutations in 93 members of 34 families of Czech or Slovakian descent using gene amplification, hybridization with specific 32P-labeled oligonucleotide probes, sequencing of amplified DNA, and gene mapping. The G----A mutation at IVS-I-1 was found in 18 families; other Mediterranean mutations were IVS-II-1 (G----A), IVS-II-745 (C----G), IVS-I-110 (G----A), and codon 39 (C----T); these were present in 9 additional families. The G----T mutation at codon 121, known to cause Heinz-body beta-thalassemia, was present in 3 families, and the frameshift at codons 82/83 (-G), first described in the Azerbaijanian population, in 2 families. A newly discovered allele was a frameshift at codons 38/39 (-C). One beta-thalassemia allele was incompletely characterized. We observed in 2 families a T----C mutation at position +96 UTR (untranslated region) relative to the termination codon; this mutation likely is a rare polymorphism. alpha-Thalassemia was rare; only one person carried the -alpha 3.7 heterozygosity, and one other had a yet to be identified alpha-thalassemia-1, while seven had the alpha alpha alpha anti 3.7 triplication.