A new spontaneous autosomal recessive mutation alymphoplasia (aly), which causes a systemic defect of lymph nodes and Payer's patches, was mapped on mouse chromosome 11 by linkage analysis using (ALY × MSM)F1 × ALY backcross progeny (155 mice). The gene order and map distances on the chromosome were as follows (cM ± SD); D11Mit14 (AntP91a), Krt-1 −(0.7 ± 0.6) − D11Mit59 − (1.9 ± 1.1) − D11Mit52, D11Nds7 (Gfap) − (0.7 ± 0.6) − aly, D11Mit10, D11Mit13, (Ace), D11Mit58 (Myla), icam-2 − (8.4 ± 2.2) − D11Mit12. No recombinant was found among aly, D11Mit10, D11Mit13, D11Mit58 and icam-2, suggesting the possible involvement of icam-2 In the aly mutation. However, the nucleotide sequence of the icam-2 gene of aly/alymouse was identical to that of the control mouse. No difference was detected between aly/aly and the control mouse for expression of the gene by both Northern biot and reverse transcriptase polymerase chain reaction analyses. Furthermore, Immunohistochemical analysis using a mAb revealed that the ICAM-2 protein was normally distributed in various tissues. These findings Indicate that aly/aly mice do not suffer from defects of icam-2. The four polymorphic mlcrosatellite markers tightly linked with the aly gene will serve as admirable guldeposts for a chromosomal walk to the aly gene.