In vitro culture offers approaches to study cellular responses and to obtain cells tolerant to high temperature stress. The objectives of this study were to select wheat cells that tolerate high temperature stress, study cell line stability and cytogenetic characteristics, and compare protein synthesis in selected and control cell lines after exposure to heat stress. Three of 600 colonies plated were recovered after cells had been exposed to 48-degrees-C. Forty-five percent of the cells of the tolerant cell line, M48 survived when they were returned to a normal temperature (22-degrees-C) for 6 mo and rechallenged with a 48-degrees-C treatment. The control cell line exhibited 0.8% survival under this treatment. Chromosomal elimination and genomic rearrangements were observed extensively for the cell lines before and after heat selection. Heat selection did enhance the occurrence of polytene chromosomes and the frequency of extrachromosomal DNA. When cell viability was evaluated in cell suspension cultures, M48 had a higher percentage of viable cells than the control cell line. Analysis of S-35-methionine in vivo labeled proteins showed that the selected M48 cell line maintained the synthesis of most normal proteins under a heat shock of 40-degrees-C for 4 h, with synthesis of several unique low molecular weight heat-shock proteins (HSPs). A quantitative increase in high molecular weight HSPs was also observed in this cell line. This study demonstrated that a heat-tolerant cell line of wheat can be obtained from in vitro selection, and that this phenomenon was associated with the synthesis of specific proteins under heat stress.